let say, we got the name "Stephen Hawking" and we often heard "Prof Hawking" and not "Prof Stephen"?
in Asia, we always use first-name (or given name) after title.
is surname often put after title like Prof or Dr?
Formally, we use last names (family names) after titles such as Dr. or Prof.:
Professor Smith and Doctor Jones will attend the conference next week.
Using a first name instead of a last name is unusual. It would be regarded as somewhat playful, and often denotes familiarity. You wouldn't see it in formal writing, but you do sometimes see it with celebrities:
Most Wednesday mornings, I watch Judge Judy right after Dr. Phil.
I've never heard anyone refer to Stephen Hawking as "Professor Stephen." The only context I could think of where that might be appropriate is with one of his graduate students, and, even then, the student would have had to build up a very strong rapport with his esteemed advisor (unless, of course, Dr. Hawking prefers to be on a first-name basis with all of his students). But, in English, that's not the way we normally refer to Nobel laureates and other greats.
I would say that using a title with a first name is akin to using other informal nicknames such as "Doc". In most situations, I'd avoid being the first to use such language; it could be considered impolite depending on the circumstances. However, I've known a few folks who have been uncomfortable with formal titles, and prefer something more informal on a face-to-face basis.