In Klingon? None.
Klingon does not mark tense (e.g. past, present, future); instead, it marks only aspect (e.g. continuous or completed).
In this case the verb has no aspect marker and we translate this with any of English’s simple tenses on this course, e.g. I walked - I walk - I will walk.
In English, I'm walking can mean a couple of things.
It can mean that walking is the type of activity I'm assigning to myself. There isn't enough room in the car. Bob is riding and I'm walking. This is jIyIt. Basically, if you could say I walk and only sound a bit archaic, but not wrong, then you need jIyIt.
It can mean walking is your ongoing activity. I'm walking for another five minutes. This is jIyIttaH or jIyItlI', depending on whether you want to express that there's a known stopping point.
Unfortunately, this Duolingo course does not distinguish between these English meanings. Anywhere you see -ing, you pretty much always have to use -taH or -lI'. This is not really correct, but you'll have to answer that way to get the course to accept your answers.
The primary source of grammar is The Klingon Dictionary. There are other sources, and many example sentences and passages written by Marc Okrand.
This is also partly a problem with understanding English grammar. We native English speakers often use our grammar without really understanding it. For instance, English often requires the use of a progressive tense even when the word being used is not really continuous in any way. The grammars of English and Klingon do not have one-to-one, rule-for-rule correspondence. When translating, you have to translate the meaning rather than the literal words.