As is showed in the title. I know: What is your major? What do you study for your bachelor's/ master's？ Are there any other ways we can use to ask others' major?
"Could you tell me your major?"
"What are you studying?"
"My major is Major. What's yours?"
"What are you majoring in?"
"Your major is?"
"We've been talking all this time and I don't even know what your major is yet!"
"Hey, I'm Name." "Hi Name, I'm Name." "Major?"
"What major are you?"