thanks, and yes some are close to him , some have been with sensei since the beging , and he seems to run it kinda family like but I still kinda not sure , thans for ansering you guys

I agree with Daniel. It depends. You can always start out with very easy, polite greetings, and non-intrusive questions. For instance, "Did you have a nice trip?" If your sensei feels like answering with any details, he can, but he could also just say "Fine, thank you." It's not a rude question. On the other hand, I would not ask "What did you do on your trip?" If you don't even want to ask a question at all, you could always just say "I hope you enjoyed your trip. It's nice to have you back."

It depends on the sensei. Always look to the sort of sensei that you have. Many don't keep themselves apart from their students. There is always a certain degree of seperation, because he is your teacher. He is your teacher and he deserves your respect, but that's it. He is still a person. Do you see other students talking to the sensei? If so, then you can likely feel free to talk to the sensei. You shouldn't interrupt him during class, but that doesn't mean you can't ever talk to him.