First off, it depends on what she likes. She will must likely love some of these:
Anything expensive really.
It depends how long you've been dating her. If it's less than a month - no. Over six months, ask her if it's okay. More than a year - definitely.
No, Not if he has another girl
Birthday gifts should be purchased in time for the person's birthday. Normally belated birthday gifts are fine with a good excuse, but it might be awkward to send a gift more than a couple weeks after a birthday.
Buy him a gift! than he will remember that he didn't give you one.
If you're concerned about him give him a call and talk to him. However he is no longer any responsibility of yours so a gift is not required, in fact it may be seen as having ulterior motives.
Well when buying a guy a bithday present you should buy him some thing like a gift card
No!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Gift certificates are not too impersonal to give for a birthday gift. They allow the recipient to buy what they really want.
If it is a girl you should buy her a necklace or a ring. If it is a boy you should buy him a video game. It really depends on the person. You could get them something related to a hobby they have, a gift card, or something you know they want.
OF COURSE NOT!!!!! matter how well they know you if they don't invite you to their birthday party then don't feel obligated to get them a gift and if they tell you later that you forgot their birthday then tell them you weren't invited to the birthday party. End of conversation!
Yes. It would be nice of them to do that but not every coworker will.
Tell them to surprise you. A birthday present should be something unexpected and surprising.