How to check date of last change in stored procedure or function in SQL server

This is the correct solution for finding a function:

SELECT name, create_date, modify_date
FROM sys.objects
WHERE type = 'fn'
AND name = 'fn_NAME'

Try this for stored procedures:

SELECT name, create_date, modify_date
FROM sys.objects
WHERE type = 'P'
AND name = 'myProc'

SELECT name, create_date, modify_date 
FROM sys.objects
WHERE type = 'P'
ORDER BY modify_date DESC

The type for a function is FN rather than P for procedure. Or you can filter on the name column.