Question

how can i know if the person who has asked the question is online or not?

Answer 1

the question itself doesnt need the person to be online to receive an answer :)

Answer 2

i do know the thing you told
but i just wanted to know, for the sake of knowledge
anyways , thank you

Answer 3

you can look on the homepage and see if he/she is there

Answer 4

Myininaya is right. You can also see if they're viewing the question on the viewers list at the top right of the question page.