Troubadour: Songweaver

Does Songweaver change the Combo trait to the Prepared trait, or does it add the Prepared trait? For example, if I were to use Songweaver to prepare Haste on myself, could I also use Oracle: Chain Spell to increase the number of targets for the Hasted spell, or can I not because they both have the Combo trait?

It adds the Prepared trait - it still can't be used to combine Combo abilities.

Songweaver
This ability allows the character to cast
Combo spells as Prepared spells. Doing so
requires her to spend the full casting time for
the spell, but causes it to affect the following
three spells she activates, excluding Combo
and Reaction spells.
Continuous

I'm having difficulty understanding the language and imagining what this skill does, to the point where I feel that trying to type here how I think it works would be counterproductive and confuse people more.

What would be a correct example of casting time, spell slots spent, and resulting attack/combos?

Let's use Enigmatic Strike (Cacophony) as the "normal" spell and Haste as the "combo" spell for the sake of simplicity.

Ordinarily, Haste wouldn't have any cast time, because it would be activated simultaneously with Enigmatic Strike. For example if your E. Strike cast time is 5 seconds, you would spend 4 seconds to caste "Haste Cacophony," or if your E. Strike cast time is 3 seconds, you would spend 2 seconds.

Let's say you know Haste from one Casting list. This would mean the "full cast time" would be 5 seconds. So you would first spend 5 seconds casting Haste. Once you do that, it functions as a Prepared spell and affects the next three spells you cast (that it would have an effect on - you can't use Haste with other Combo or Reaction spells, so exclude those.) For example: if you cast three E. Strikes in a row, each would benefit from the -1 second cast time.

However, since it is a Prepared spell, you would need to use all three within five minutes of taking any action once it's cast, or the effect would expire.