>>95845150
Easiest one is:
>"What do you want to do when you sit down to play this deck?"

Ask him if he's even looked at his own deck.
Literally just start pointing to cards and ask:
>"What does this do? In the context of your deck? What cards synergize directly with it? What turn does it do that effect at it's earliest? How consistent is getting it off?"
Don't need to really listen to any words he's saying either if you can't be assed, just listen if he's scrambling for an answer, or has actually thought about it.
And try:
>"Have you goldfished or tested this deck?"
>"Assuming nothing at all happens, do you have a threatening boardstate and or hand by turn [depends on whatever bracket or powerlevel you play]?"

99% he can't answer jackshit. First part is making him admit that. Naturally, don't shittalk him for admitting that. Deckbuilding can be pretty overwhelming for noobs since most cards just seem pretty functional.
Then you can ask things like:
>"What boardstate do you want to achieve by turn 6-7? Name the actual cards, both in hand and on board"
>"What's the perfect opening hand for you?"
>"Goldfish your deck 10 times. Compile how your hand and board look at turn 7. Are you hitting all 7 lands? If not, how many out of 7? From which turn do you start missing them?"
And when he still can't answer the first two:
>"Why the FUCK did you make this deck if you clearly don't care? WHY did you pick the commander? WHY did you put ANY of the cards in the 99? If you can't answer any of these, you should simply abandon the deck"
In the case he CAN answer that he picked Pantlaza because he wants to play dinos and turn them sideways, you can start from the top again. Eventually, he'll break from the cycle if he's committed.

I probably did not word this in an ideal manner. But this helped me tune my own decks and helping me teach my noob friends how to deckbuild.
Best of luck anon.