How to find exact point for a tcode

Hi Experts,

I have to find out exact point in Tcode- VT02N and ME22N,Means i need while we go for me22n which subrutine is calling like example if we go for VA02 then PERFORM USEREXIT_READ_DOCUMENT subrutine is calling similar to i want to know for Tcode - VT02N and ME22N also,If anyone face same requirement can help me.

Thanks,