Can't get sks trigger assembly back in

Check that the magazine is in correctly.

Assuming it is seating properly many of them are tight as they cam in to lock . If the trigger group is setting flush down on the stock and the receiver is properly set in the stock rest the reciever on a hard surface ( such as a work bench or a scrap 2x4 not a cement floor ) and sharply rap the trigger guard with your palm driving it straight down to the lock position . Some are tight due to tolerances , and others are tight due to tolerance stack , even excess cosmo can make things hard to reassemble . Its a com block battle rifle tho and as such sometimes things get sticky.. I wouldnt put it on a tree stump and whack it with a piece of firewood like i am sure has been done in the past , but about anything short of that would be game .

Check that the safety in on. Else it blocks the latching mechanism, and you can break the safety spring if you try to force it all back together with the safety off. Ask me how I know.

I find that the force required to get the trigger assy to click into place is substantial. As per the above, be sure the mag and all else are really in place. However, it may be easier to swing the mag open and verify that the pins on the assy front end are going into the slots in the receiver bottom.

I usually hold the rifle on the floor with the trigger assy up, and force down with both hands to get it to latch.

Always happened to me too. What heppened is the receiver wasn't set in the stock all the way because it would be pushed out a bit when flipping the gun over and pushing the trigger gaurd in. Now I turn the rifle over and put the reciever on a hard surface so it can't be pushed out of the stock when pressing the trigger guard in.