hi,
is it possible to show the grades of all students in an activity to students?
What I want is that when a student clicks on "report" he can see the results of all enrolled students, not only himself.
Yes that would be possible. But this would be strictly a custom module (you could make it an activity or a report). If you're asking to know if you could do it, the answer is yes, but you'll need to get acquainted with how to retrieve that information out of the database (topic in itself) as well as how to build a plugin module for Moodle which is also quite a long topic considering all the embellishments along the way with event hookup, contexting, UI forms (there's a forms interface object list to work with and you'll need to get familiar with how that all works too) etc. If you want to go down that road I suggest first checking out the online documentation that is provided by Moodle for developing your own plugin module and also to check out the developer forum(s) and post development related questions there pertinent to development of your module.
You can find your development documentation direction by topic here:
https://docs.moodle.org/dev/Plugin_types
Hi,
I've not investigated myself, however I suggest you try allowing the capability gradereport/grader:view for the role of student. You may need to allow more capabilities too. See the documentation Permissions for more details.
You can always test things first on the Moodle Sandbox demo. Log in first as an admin, change permissions then log out and log in as a student (or log in as a student in a different browser) to check.