If you already have wkof installed (if not: Installing Wanikani Open Framework), then go to the WK site, open the javascript console (F12, Ctrl+Shift+I, or Ctrl+Shift+J), go to the console tab, then run
await wkof.include("ItemData")
console.log((await wkof.ItemData.get_items({wk_items: {options: {assignments: true}, filters: {item_type: 'voc', srs: '5,6,7,8,9'}}})).map((item) => item.data.context_sentences).flat().map(sentence => sentence.ja).join("\n"))
This assumes your definition of “known” is anything guru I and above. It should result in a large piece of text right after (it will be cut off by …), just right click and copy it, then paste it into your favourite text editor. This is the japanese sentence of every single context sentence from vocabulary words you in theory know.
If you want a different format, just say it.