If I got employer-provided assistance for school, where can I find that on my W-2?

The amount of employer-provided educational assistance is generally not shown on your W-2. It is simply omitted from the total wages in box 1.

Your employer is not required to report that anywhere on your W-2.  Some employers may show it in box 14 or (less often) box 12.  Your pay stub is the most likely place to find documentation of the reimbursement.

By law your employer can only give you $5250 maximum, tax free. If your tuition was less than that, and you employer reimbursed it all; it’s  safe to assume it does not need to be reported. 

 If you got more than $5250, the amount above $5250 is usually already included in box 1 of  your w-2 and you do not need to enter anything additional on your tax return.