If I am sick and out of office for a day or two. And if my colleagues have sent me wishes, Should I reply back to each "get well soon" email Once I return to the office?
If yes, how should I reply to them? Can anyone please let me know about this?
You are not forced to write back to them when you get back, but yes I get it that it can be a nice gesture to thank them.
Two things I can think of are:
Again, you are not forced to thank every one of them. If the task of thanking each and every single one of them would take much time then consider doing option 1 and 2.
If the number of mails you've got is manageable in reasonable quick time, and you feel like it, then go ahead and reply to each of them, one by one.
When replying, feel free to thank them as you wish. There is no rule for this, as long as it is honest. You can be brief like "Thanks guys, I am feeling well and back at the office now. See you soon", or something you feel comfortable with.