>I only see, that thrugh SERVER MANAGER i can see the open resources, but it is very difficult examine all those resources.
>I would like to select a file and know the users that are using that file at that moment.

I don't know of a direct way with SM - you can narrow it down by looking at the number of users in SHARES, at least, and then looking at IN USE.

That said, the timing of files open/close is delayed a little and not perfectly accurate at any exact second, either.

You may need a third party tool to get more specific, or build your own with vfp, even.