Learn Danish: Jeg er godt klar over at det er svært. - I am well aware that it is difficult.

In Danish, the fixed expression for "to be aware of" is at være klar over. Prepositions rarely translate one-to-one between English and Danish. You simply have to memorize over as the required preposition for this phrase.

Could I use meget instead of godt to mean "very aware"?

You could be understood, but godt klar over is the standard, highly idiomatic way to express being "well aware" or "perfectly aware" in Danish. Using godt here functions as an intensifier and sounds much more natural to a native speaker than meget klar over.

Why isn't there a comma before at in this sentence?

It depends on which Danish comma system you follow. The traditional "start comma" rules require a comma before a subordinate clause, which would look like ...klar over, at det er svært. However, the Danish Language Council recommends omitting the start comma, which is why it is missing here. Both choices are officially correct.

Can I drop at, just like we drop "that" in English ("I am well aware it is difficult")?

Yes! Just like in English, the conjunction at is frequently dropped in casual, everyday spoken Danish, so you will often hear Jeg er godt klar over det er svært. However, at is usually kept in written Danish.