Wallabag is a Pocket-like read it later service. One that you can host yourself (pretty much like mastodon vs twitter, gitlab vs github or weblate vs transifex). There're also people that offer access to their wallabag instances, so you don't need to run one yourself.
But wallabag has nothing to do with pocket. Your pocket articles can't be retrieved with wallabag.
Pocket is one of the most popular read it later services. Sadly, the way it works in kobo doesn't make articles readily available to other programs.
If you want to read pocket articles in KOReader the best bet is using a calibre recipe (
https://github.com/mmagnus/Pocket-Plus-Calibre-Plugin) an transfer the result using USB or wifi.
I never tested the calibre-pocket recipe, but seems well maintained.