the first phrase "excuse me sir, can i ask a question" is something you can but is very formal and would be used anywhere that speaks english. The second phrase doesn't really make sense and isn't a question. You would say "Sir, I would like to ask you a question" but it is a phrase - similar to saying something like "I want an ice cream" Just go with the first option. Hope this helps and good luck :)

The first one is correct, the second one should be “I would like to ask you a question”.