You need to the enter the sale of home in schedule D, just like a stock transaction. and that is where the gain will "really" come from. Theoretically it will match the amount on the 8288
The withholding goes in the Miscellaneous > Statement of Withholding ... 8288-A and that will carry as withholding to the 1040 (or 1040NR)
Here's wishing you many Happy Returns
Just to add to George's helpful response, you will need to obtain from your client details of the transaction from purchase to sale like you do with your domestic clients. You will only be able to extract the amount for gross proceeds but not much else from F.8288 or F.8288-A because those details are not required - if your client had filed a F.8288-B, that would be more helpful.
The input you make for F.8288-A will flow to 1040-NR but not 1040, if that's what your client files.
Still an AllStar