How to become a moderator?

I don't know of any way to apply for such a position.  I always assumed it was by invitation only.

Be careful what you wish for.  Stock Reviewers are expected to evaluate 500,000 assets per week. 

You should check out the Adobe Human Resources pages. The forum is the wrong place for looking for job offers.

There is no way to offer your services or apply. Members here speculate that there are hundreds of moderators, and they may not be based in the US or Europe; we don't know if there is a preferred first language and whether it is English. They might be employed by a third party. They will have to work to very strict schedules and follow tasks very precisely so the team can get through hundreds of thousands of submissions in a week.