With the extension or any other suitable rod that won’t leave anything in the combustion chamber (not a stick). As the piston rises, it will rise. The highest point that it sticks up is TDC. Your T in the window will probably be a little before that. The crank makes 2 revolutions while the cams make 1, so your cams determine which stroke the engine is on. This is why you roll the crank twice by hand to check your timing. If you only roll it once, the cams will be way off.