C - SUBSET functions do not exist in spreadsheets, so the syntax is not obvious. Basically you chose a field and function like a subject/ verb, then a clause that defines which subset of the rows you want to consider, like this:

"Count all the (non-blank) EmployeeIDs where the Category value in the same row is X"
SUBSET_NONEMPTYCOUNT([EmployeeID],SUBSET([Category], "X","="))

To break it down by each Country:
SUBSET_NONEMPTYCOUNT([EmployeeID],SUBSET2([Country], [Category], [Country],"X","=","="))

Notice that you want all values for [Country], so you must include [Country] all values a second time as a placeholder so that the Formula knows that the match value "X" corresponds to the field [Category] in the order.

More detail on SUBSET function syntax is here:
http://www.visokio.com/kb/subset-functions