The rich young ruler was brought up in argument and instead of going back to find the post to address it after I've formulated my rebuttal, as I sort of skimmed considering it no new argument having heard the same argument reasoning repeatedly, I will address it in general here, considering that he display this lack of faith in asking, "What must I do?" I would go back and review the context for instances that Jesus was teaching when this man approached Him with this inquiry. I'm fully certain that He was teaching but exactly what, I'd have to refer back to the context (and I'm being lazy this morning since I've yet to step onto the cold floor to start a pot of coffee).
So, I'll make an educated guess that Jesus was teaching something similar to "God's will is that you believe on the Son" or "This is the work of God, that you believe..." and this young ruler wasn't paying that very much attention when he interrupted Jesus. But, Jesus, loving him, and full of grace, 'suffered him the indulgence' (I now have a cup and a Danish as I made use of the time formulating the best wording for that) and 'met him where he was when he said, "(Yes) You know all the commandments... (and I'm fully aware that you think you've kept every one of them since youth. And I have no doubt that you will be glad to tell me this...)
On the other hand, the thief of the cross didn't ask this question. I don't think that he asked any questions as a matter of fact

He simply pleaded, "Remember me..."