Is there a way I could querry or sort out duplicate enteries by social
security number from a large excel sheet.

Here's one way.

If the SSN is in column A, select column A and use:
Format Conditional formatting

From the pull-down choose "Formula Is" and use
=COUNTIF(A:A,A1)1

Then click on "Format" and choose a "pattern" to appear in the duplicate
cells.

Then click OK and OK.