Since I couldn't find any documentation on that, here's a little help for people who are trying to use osc to control kluppe. The relevant file for osc is src/common/osc.c. The possible commands are implemented in lines 117-192.
Now, a little example how to make kluppe play the first looper:
oscsend localhost 1784 /kluppe/loop/1/Play i 1
The path /kluppe/loop should be the same for all messages, 1 is the looper index (starting at 1), Play is the command (all commands are implemented in the osc.c file), i 1 means that there is one integer parameter, 1, which means that the play status should be 1 (= playing).
Another example, setting the volume to 0.1 (a float):
oscsend localhost 1784 /kluppe/loop/1/Volume f 0.1
Loop indices start at 1. If you pass 0 as a looper index (/kluppe/loop/0/...), you control all existing loops.