For what purpose?
There is a mark on the crank pulley that indicates TDC.
Keep in mind that there is TDC compression and exhaust. For most purposes you'll be shooting for compression. If that's the case, I prefer to install a compressor tester hose, and bump the engine over until air blows out of it. Then insert your screwdriver and rotate the engine until the piston is at the top.
If the valve cover is off, you can also observe the valve behavior prior to TDC. Just before compression, the intake valve will open.