Ohhhh, now I see what you mean!
Some people do use KaniWani for that purpose. They use a handwriting-based IME or just write it down on paper. But there is no sensible way to make KW put up kanji instead of vocab. KameSame has the option to include kanji, but there’s no way to exclude vocabulary as of now. You could ask in this thread.
You could also export your WaniKani deck to Anki or another SRS program, since you’re manually testing yourself. Since you can just export all the kanji, this is probably the best option. WaniKani to Anki Exporter - http://wanikanitoanki.com
(If that one doesn’t work, try https://wanikaniexplorer.com/ – sorry, never exported my deck)