There is a lot to unpack here. Firstly, let’s start with the dangerous:

Dangerous

Your code is wide open to injection attacks. This is incredibly dangerous. You are injecting your parameters into your statement, making it insecure. Your use of EXEC(@SQL) syntax doesn’t help the matter as it makes it impossible to parametrise your statement. Use sys.sp_executesql to execute your statement and parametrise it.

Deprecations

You are using FROM <TableName> (<Hint>) syntax, which is deprecated. It should be FROM <TableName> WITH (<Hint>), however, speaking of your table hints…

(Ab)use of NOLOCK

You’re (ab)using the NOLOCK hint here. Aaron Bertrand covers this subject in depth in Bad habits : Putting NOLOCK everywhere, however, you likely don’t need any of those hints. If you "must" (which I strongly doubt) use it change the isolation level, don’t spam the hint against every table.

Non-SARGable clauses

Almost all your clauses aren’t SARGable. Queries with a leading wildcard can’t use indexes and almost all of your clauses do this. One of the only that doesn’t, against specialtyId CASTs that column to a varchar making it also non-SARGable. If you didn’t inject your value, perhaps you could parametrise it with a valid data type.

Everything but the kitchen-sink

What you have here is known as a "Catch-all" or "Kitchen Sink" query, however, you don’t handle the problem well. You still check the value of every variable but if you’re using dynamic SQL then you should only pass the variables that have a non-NULL value (you are using NULL rather than '' for "no value, right?). As you’re using a dynamic statement, I continue down that route.

Implicit INNER JOIN

Your LEFT JOIN to Jackie was an implicit INNER JOIN as its column id had to have a non-NULL value in the INNER JOIN to jackieSpecialty. Don’t use LEFT JOINs for tables that must have a value returned from them.

Formatting

The formatting needed a lot of work too. Syntax like ''''Application is very confusing (remember that’s in a dynamic statement). Use AS or = syntax such as '''' AS Application or Application = ''''. Not to mention many of your statments were on a single line and are hard to read.

Incorrect Alias

Your derived table was alaised as tl but your outer SELECT references t.

Solution

This is untested apart from to check that it creates a valid statement, but for some of your parameters should be faster (@Specialty and @Phone). For others, it might be, as I make the query only pass the clauses for the variables that have a non-NULL value (note NULL, not ''). As mentioned, leading wildcards aren’t SARGable, so if you need better performance, you should reconsider if you should really be using them here.

This can’t be tested against your table, and the data types for variables are guessed. Use your best friend to help debug this if you encounter errors (I’ve done too much here in my opinion):

--All following datatypes are GUESSED
DECLARE @FirstName nvarchar(50),
        @LastName nvarchar(50),
        @Phone varchar(15),
        @Email varchar(100),
        @Specialty int = 5,
        @AdditionalLicensedStates varchar(10),
        @DesiredLocation varchar(50),
        @CompactState varchar(5);

DECLARE @query nvarchar(MAX),
        @CRLF nchar(2) = NCHAR(13) + NCHAR(10);
SET @query= N'SELECT t.CandidateId,' + @CRLF +
            N'       '''' AS Ranking,' + @CRLF +
            N'       t.[Status],' + @CRLF +
            N'       t.FirstName,' + @CRLF +
            N'       t.LastName,' + @CRLF +
            N'       t.Phone,' + @CRLF +
            N'       t.[Email],' + @CRLF +
            N'       t.ID AS TroveId,' + @CRLF + 
            N'       t.Desired,' + @CRLF +
            N'       t.Licensed,' + @CRLF +
            N'       t.Specialty,' + @CRLF +
            N'       t.CallBack,' + @CRLF +
            N'       t.LastContact,' + @CRLF +
            N'       t.LastContactNote,' + @CRLF +
            N'       0 AS MatchingJobs,' + @CRLF +
            N'       t.AvailableDate,' + @CRLF +
            N'       t.DepartmentId,' + @CRLF +
            N'       0 AS  DocumentId,' + @CRLF +
            N'       '''' AS Division,' + @CRLF +
            N'       '''' AS EMRSystem,' + @CRLF +
            N'       '''' AS Application,' + @CRLF +
            N'       t.Compactstate ' + @CRLF +
            N'FROM (SELECT T.CandidateId,' + @CRLF +
            N'             T.Status,' + @CRLF +
            N'             C.FirstName,' + @CRLF +
            N'             C.LastName,' + @CRLF +
            N'             C.Phone,' + @CRLF +
            N'             C.Email,' + @CRLF +
            N'             T.ID,' + @CRLF +
            N'             T.DepartmentId,' + @CRLF +
            N'             j.DesiredStates AS Desired,' + @CRLF +
            N'             j.Licensed,' + @CRLF +
            N'             j.Specialty,' + @CRLF +
            N'             T.Compactstate,' + @CRLF +
            N'             j.AvailableDate,' + @CRLF +
            N'             cb.CallbackDate AS CallBack,' + @CRLF +
            N'             CONVERT(date,n.DateCreated) AS LastContact,' + @CRLF +
            N'             n.Notes AS LastContactNote' + @CRLF +
            N'      FROM dbo.TreasureTrove T' + @CRLF +
            N'           INNER JOIN dbo.Candidate C ON T.CandidateId = C.Id' + @CRLF +
            N'                                     AND T.DepartmentId = 1' + @CRLF +
            N'                                     AND T.Profile = ''0''' + @CRLF + --If this is 0, why not compare to a literal int?
            N'           INNER JOIN dbo.ProfileLinked P ON T.CandidateId = P.TroveCandidateId' + @CRLF +
            N'           INNER JOIN dbo.Jackie j ON j.CandidateId = T.CandidateId' + @CRLF + -- As j.Id must have a non-NULL value, changed to an INNER JOIN
            N'           INNER JOIN dbo.jackieSpecialty js ON js.jackieId = j.Id' + @CRLF +
            N'           LEFT JOIN dbo.Notes N ON N.ObjectID = T.CandidateId' + @CRLF +
            N'                                AND n.IsLatest = 1 ' + @CRLF +
            N'                                AND n.Category = ''3''' + @CRLF + --If this is a 3, why not compare to a literal int?
            N'                                AND n.NoteType = ''NormalNote''' + @CRLF +
            N'           LEFT JOIN dbo.CallBack cb ON cb.CandidateId = t.CandidateId' + @CRLF +
            N'                                     AND cb.IsLatest = 1' + @CRLF +
            N'                                     AND cb.CallBackType = ''Trove''' + @CRLF +
            --I'm suggest you pass NULL for your parameters, not '' when you don't need the, I assume they are NULL below
            NULLIF(N'WHERE ' + CONCAT_WS(@CRLF + N'  AND ',CASE WHEN @FirstName IS NOT NULL THEN N'C.FirstName LIKE ''%''+@FirstName+''%''' END,
                                                           CASE WHEN @LastName IS NOT NULL THEN N'C.LastName LIKE ''%''+@LastName+''%''' END,
                                                           CASE WHEN @Phone IS NOT NULL THEN N'C.Phone = @Phone' END,
                                                           CASE WHEN @Email IS NOT NULL THEN N'C.Email like ''%''+@Email+''%''' END,
                                                           CASE WHEN @Specialty IS NOT NULL THEN N'Js.specialtyId = @Specialty' END, --Don't CAST/CONVERT your columns. I guess the data type here later.
                                                           CASE WHEN @AdditionalLicensedStates IS NOT NULL THEN N'J.Licensed LIKE ''%''+@AdditionalLicensedStates+''%''' END,
                                                           CASE WHEN @DesiredLocation IS NOT NULL THEN N'J.DesiredStates LIKE ''%''+@DesiredLocation+''%''' END,
                                                           CASE WHEN @CompactState IS NOT NULL THEN N't.CompactState LIKE ''%''+@CompactState+''%''' END),N'WHERE ') + N') as t';    
PRINT @query;-- YOur best friend

EXEC sys.sp_executesql @query,
                       N'@FirstName nvarchar(50),@LastName nvarchar(50),@Phone varchar(15),@Email varchar(100),@Specialty int = 5,@AdditionalLicensedStates varchar(10),@DesiredLocation varchar(50),@CompactState varchar(5)', --Remember, these are all guessed
                       @FirstName,
                       @LastName,
                       @Phone,
                       @Email,
                       @Specialty,
                       @AdditionalLicensedStates,
                       @DesiredLocation,
                       @CompactState;