Ka is shown on my rhythm notations as “K”.
Ka is an essential tone for more advanced playing. It is typically an ornamentation for the basic rhythms. Ka and Tek used together form the basis for most rolls on the doumbek.
Ka is played with your off hand. The off hand and arm rest on the top of the drum, relaxed and with your fingers straight, but loose. Lift your hand up and let it fall onto the edge of the drum, striking on the padded bottom of your palm. This should snap your fingers down onto the rim of the drum head. The important thing is to only strike with the ring finger. Keep the index, middle, and little finger up and out of the way. The resulting sound is a sharp, snapping KA, with no sustain at all. It is similar, but not quite the same, as the TEK. Do not strike too hard, as it can hurt. Be patient and develop your hand strength and flexibility. The looser your fingers are, the easier this technique becomes. Getting your ring finger to strike the perfect spot to maximize your sound, and learning to keep the other fingers out of the way, is very challenging. To get a clear, sharp, and consistent Ka takes most drummers months, if not years, of daily practice.
As always, there are a ton of video clips out there, so by all means, type “Ka” into your favorite video search engine and get a visual of what I am describing.