Can you cast a sorcery-speed spell during your second main phase after attacking?

A turn's structure includes two main phases: the first main phase (before combat) and the second main phase (after combat). Both are full main phases with identical rules about what you can cast. Specifically, CR 505.1 establishes the second main phase and CR 307.1 states that sorceries can be cast any time you have priority during your main phase when the stack is empty.

After combat ends, the game moves into your second main phase. At the start of this phase, active-player priority is granted (CR 117.3a). As long as the stack is empty and it is your main phase, you may cast sorceries, play lands, and take other sorcery-speed actions, exactly as you could in your first main phase.

The key conditions are: (1) it must be YOUR turn, (2) it must be a main phase, and (3) the stack must be empty when you attempt to cast the spell. All three are satisfied at the start of your second main phase.

Example: You attack with a 3/3 creature, combat resolves, and you move to your second main phase. You may now cast a sorcery like Divination to draw two cards, just as if you were in your first main phase before combat.

This is actually a common strategic consideration — players sometimes save spells like creature removal or planeswalkers for the second main phase so they don't tie up mana during combat, having seen how the combat step resolved first.