Learn Danish: Mændene vil genopføre slaget i rollespillet. - The men want to reenact the battle in the roleplay.

The prefix gen- acts like the English prefix re-, indicating repetition. The base verb opføre means to perform (like a play) or to construct. By adding gen-, we get genopføre, meaning to perform again or to reenact, which fits perfectly with staging a battle.

Could I use genskabe instead of genopføre in this sentence?

You could, but genopføre is much more precise here. While genskabe means to recreate or restore something generally, genopføre specifically carries the theatrical meaning of putting on a performance or staging an event again. This matches the context of rollespillet (the roleplay).

Why isn't there an at before genopføre, since the English translation says want to reenact?

In Danish, vil (from ville) is a modal verb. Modal verbs always take a bare infinitive directly after them, meaning you must drop the infinitive marker at (to) before the next verb.

How is the definite noun rollespillet formed?

It is a compound noun made from rolle (role) and spil (game or play). In Danish, a compound word always takes the gender of its final noun. Since it is et spil (neuter), the definite form takes the suffix -et, resulting in rollespillet.