The usual English form is KEEN-wah, and it is the first one Oxford lists. Cambridge also lists kin-WAH for American English and kih-NOH-uh for British English. Some people say kee-NOH-uh, which Wiktionary shows for both accents.
The word is Spanish, from quinua, which comes from the Quechua word kinwa, the name of the plant in the Andes. In Quechua the first syllable is the ee of keen, and that is why English uses qui for k + ee.
The mistake to avoid is kwin-OH-uh, which comes from reading qu as kw as in quick. Here q + u + i is a k + ee. Say keen, then wah, and the word is done.