Learn Danish: Jeg er sikker på at han kommer. - I am sure that he is coming.

In Danish, the adjective sikker (sure) usually pairs with the preposition på when you are stating what you are sure about. While English simply says I am sure that, Danish effectively says I am sure on that (sikker på at).

Is the word "at" mandatory in this sentence?

In formal writing, it is best to keep it. However, in everyday speech, Danes frequently drop at, just like we drop that in English. You will very often hear people say Jeg er sikker på, han kommer.

Why is "kommer" translated as "is coming" instead of "comes"?

Danish does not have a continuous tense like the English am/is/are plus an -ing word. The simple present tense kommer handles both he comes and he is coming. You just rely on the context to know which translation makes sense in English!

Can this sentence be used to talk about the future?

Yes! Danish frequently uses the present tense to talk about future events. Depending on the situation, han kommer can mean he is on his way right now, or he will come to the event tomorrow.