Hmm… Interesting question.
I’d probably ask him to give me a vision of what Heaven looks like. No guarantee it would happen, but why not?
I’d also like to ask him to guard and protect me more. I get tempted with sin a lot, I’m not sure if Guardian Angels can do anything about this, but it’s worth a shot.
Lastly, I’d probs ask them to ask Jesus directly to talk to me and interact with me more, without the risks that come with general spiritual sensitivity (see: Padre Pio) and for him to ask Jesus to grant me the ability to detect angels in disguise, amongst other things.
Again, very unlikely some of these would happen, but you never know. Ultimately though, the best request would be to ask him to help secure and ensure our salvation.