Wow, yeah, for sure cluster by DateSent if that's the case.  The other conditions won't matter.

Btw, the other tables I was worried about being scanned, I had more...

Yep, that's fine.  The results are interesting.

1) Do you often/very often search by a SentDate range?
2) Is a 1 year range typical for a date search? ...

First thing is to make sure you have the best clustering index on the table.  Then we'll look to see if additional indexes or code changes or other things are...

You could try using a CROSS APPLY to assign the alias name, then use that alias in the SELECT clause:

SELECT ...,
    ca1.STAGE_022_COMPLETED_DATE_IS_NULL_REV_DATE,
    [dbo].[fnc_CalcWorkDaysBetween] (ca1.STAGE_022_COMPLETED_DATE_IS_NULL_REV_DATE,...

Float doesn't have nearly 60 digits of precision, does it?

SELECT REPLACE(CAST(FORMAT(CAST('123456789012345678901234567890123456789012345678901234567890' AS float),
'### | ### | ### | ### | ### | ### | ### | ###...

Basically this:

SELECT SCandidateID
FROM dbo.CandidateSkills
WHERE Skill IN (@ssrs_skill_param)
GROUP BY SCandidateID
HAVING COUNT(*) = <number_of_values_in_skill_param>

But not sure how in SSRS to get a count of...

I say keep it simple unless you really need to do something more complex:

SELECT STUFF(
    CASE WHEN SUBSTRING(column1, 1, 3) = '000'...

WHERE column_name LIKE '1[67]-Nov-2017%' /* or '%1[67]-Nov-2017%' if the column doesn't start with the day */

Edit: Sorry about the formatting.  The site automatically "adjusts" (corrupts!) multiple spaces into fewer spaces.

SELECT start_date, end_date,
  CASE WHEN start_date >= '20140101' OR...

It's wasteful to store monthly, quarterly and yearly data in a daily table (actually, it's wasteful to store days in a year anywhere, since your year is a calendar year). ...