i’ve recently started using QNX and i wonder how you mount the cd player

CD should automatically mount when you put in a CD, and it will be available in /fs, probably as cd0, this should work with data and music CDs. If you put in a music CD, see if it plays using the CD player which is located on the shelf, assuming your sound card is supported.

I now but I can’t access it from the file manager.

You mean you can navigate to /fs/cd0 in the terminal, but that does not work in the filer? That sounds a bit odd. If you’re looking for a nicer way to access it than /fs/cd0, I don’t think that exists.

I can access the cd from the cd player but not from terminal or file manager

I am not quite sure, but I think if it is a audio CD, you will not be able to see any files under /fs/cd0 though cd player can “read” it. You can only access the files under /fs/cd0 if it is a data CD.