When going to a job fair, what is the acceptable questions to answer? And when I am uncomfortable to answer their personal questions, what to say?

It’s completely understandable to feel unsure about what’s appropriate to ask or answer at job fairs. If you’re asked something personal and you’re not comfortable answering, you can politely redirect the conversation back to your skills and experience. This way, you keep the discussion professional without sounding defensive.

You might find this guide on common interview questions helpful too: 10 Most Common Interview Questions and How To Nail Them

Ok thanks

You can always reply "why do you ask?" .

What kind of personal questions?

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Usually they will ask direct questions "Would you be comfortable to travel once a month" versus "Do you have a girlfriend / wife / kid", "Do you think your loved ones would deter you from travelling"