Hi Andi!
Get the id of your partition ( e.g. /dev/sdi1)
open a command window and then:
-> sudo mkdir /media/jfsos2 (or other name to define your mount point)
-> sudo mount -t jfs /dev/sdi1 /media/jfsos2
-> If it fails, may be alignment isn't ok under linuw (I have miss aligned partition for one of all despite all where created under OS/2 ARcaOs LVM
note: To trim in case of an SSD.
Once the partition is mounted:
-> sudo fstrim -v /media/os2jfs
Hope this is helpfull