Other than going to dentist, is there any means, methods or ways to find out how bad is my bruxism when i am asleep?

Bruxism: I would say " no." if you want a definitive answer you need to get see professional help.

Sleep partner: Unless you are sleeping with your dentist, they won't be of much help. If you have a partner, get their sense of what you do while sleeping and even have them record it, audio or video to get a good answer to your question.

EMG might work but..: Nocturnal bruxing /tooth grinding is usually best detected through observation by your dentist. Sure, your partner may hear you grinding but that may have no bearing as to power of destruction that it's force and motion are doing to your teeth. Why get involved with EMG type devices when simple night guard may do the trick! see your dentist!