Should I cap off my clogged kitchen pipe at the wall or after the p-trap?
Any of those options will work, let me reorder them to:


Easy option: Cap off the sink hole &amp; garbage disposal. 
Leave the P-Trap and cap the pipe off after that.
Remove all the pipes under sink &amp; garbage disposal and cap off main pipe at wall.


Now they're in order of ease and how temporary you want. If you want to simply stop the sewage fumes, the P-Trap (filled with water) will do just that so #1 &amp; #2 will do that. #2 &amp; #3 are good but might be a bit overkill especially if you leave the sink in place, even with the sink faucet off you'll have the occasional pot drained/strained in the sink and glass dumped in there. So if you have any drainage left, I'd just leave it and probably just turn off the faucets. If not, personally I'd removed the P-Trap back and cap it, then put a 5-gallon bucket under there.