@dwi-di apologize for the very late response. Could you solve your issue?
As @ijohnson mentioned, $SNAP_USER_DATA is the per-user writable area for a particular revision of the snap (in this case something like /home/you/snap/kafkactl/current). And $HOME is set to $SNAP_USER_DATA for all commands.
You can find further documentation about the personal-files interface here. The Security policy and sandboxing documentation is very helpful as well to get a further understanding of confinement, policies, env setup, etc.
Let us know if you have any further question!