I'm mounting an iso-file. Finder shows the name as "This Product" but the folder-name is /Volumes/this_product_" or could be something else.
How can I retrieve the name as shown in the Finder?
It depends on what you are using it for (just for manual lookup or for parsing).
In Applications -> Utilities -> Disk Utiltity you can just mark the partition (not the whole volume) and at the bottom of the window it will show the mount point.
If you need output that can be parsed somehow here are two ideas:
1) diskinfo list gives you a list of all disks in the system. And with the partition names on the disk your're looking for you can do an diskutil info disk1s1 (replace disk1s1 with the actual partition name) which will list the mount point.
2) Alternately, if you know the name and location one file on the mounted volume, you could do an ls /Volumes/*/thatfile and you'll get output of the volumes folder where it is found.