How I know about the amount of 'revenue share' earned from this forum.

do you mean generally or specifically yours?

Taken from the FAQ:
http://www.webmaster-talk.com/faq.ph...sense_faq_item

Ad Revenue is shared between the Administrators, the new Thread Starter and the last replier in a particular thread.

As a new thread starter, there is a 40% chance your Adense Code will be displayed for each page view. The last replier in a particular thread will have a 10% chance that their Adense Code will be displayed for each page view and the administrators have the final 50% chance.

This should encourage both new thread posting in addition to participation in other member's threads.