First finish up at slag heap, checking in with diode before making your way to the second floor for that important chat with korshunov, and definitely think through your choice about the unusual pda since it matters later. Once you're done inside, you'll find richter hanging around outside - make sure to exhaust his dialogue completely, otherwise things might get weird later. The sawmill's southeast on your map and you can't miss it with all the destroyed buildings and military vehicles around. Inside the main building, you'll find scar waiting to have another chat about that pda, and whatever you decide here is gonna stick with you for a while.

Tip if things go wrong: sometimes scar decides not to show up which is pretty annoying but fixable. Just hit the key to open console, type in XResetQuestBySID E03_MQ06 and you should be good to go without breaking anything else in your save.