You'll want to ask for the final checkstub of the year and hope its got the OT Y-T-D figures on it.   Then scroll down to Page 2, I think its Part III on the W2 worksheet for the OT entry area.

Ive got a guy that his final stub doesnt have a YTD, so hes grabbing all his weekly stubs that show it and adding them up before bring them to me.