If your friend is on chess.com show him these endgame courses in Chess Mentor. There are also some videos and exercises on endgames in the Study Plan Directory. Chess Tempo has an endgame trainer, but it may be a little more advanced than what you have in mind.
Practicing endgames 101 using Chess.com

It's important to get lots of practice with these, and I have found the best way to train is to play, again and again, against the computer. Sure, it may be helpful to go through those lessons, but I 'derived' the principles through practicing against the computer. Chess.com previously was a great tool, because if you ever needed some help, you could turn on the computer which told you "there is a checkmate in 4 moves" or "since the score dropped down, your last move was a mistake".

Ask our Mod friend... KRFenigma

I hate to send you off-site, but I guess sometimes it is necessary.
Here's another endgame simulator :
http://www.chessgym.net/flash/exercises.php
Sign in as guest, and then the menu has an endgame simulator that you can set up as you wish.
Hi there,
I am teaching someone who is completely new to chess first principles of checkmating. So King&Queen vs King; King&Rook vs King; two rooks & king vs king; etc.
I learned these by using the Chess.com app as it, in a previous version, had practice endgames where you could set the conditions (eg. two bishop checkmate), but it seems like in the new version of the app this functionality has been removed
. The 'change set-up' function was also removed, so you can't even do it this way.
When I first began playing a year ago, I learned the principles of checkmating a king using the Chess.com and I found it really useful.
This is the only alternative I have found so far: http://www.chessvideos.tv/endgame-training/king-and-queen-checkmate.php
1) Any advice on where my friend can practice this?
2) Why can't Chess.com bring this feature back?