They imprisoned the wife who is ruler of different country. How to get her back

The main purpose of Prestige is to add to your Dynasty Score: this shows how powerful and successful your dynasty is. If your final Dynasty Score is higher than your buddy's Dynasty Score, you're a better ruler than him. You are usually going to get a lot more Prestige than you can spend over the course of a ruler's life.

That said, there are a few things you can spend Prestige on, though none of them are particularly expensive, unless you're a new ruler of a young dynasty or otherwise poor in prestige:

1. Creating an Antipope costs 500 prestige.
2. Marrying one of your kids to someone of lower rank than your kid reduces your kid's prestige; it costs -100 prestige per difference in rank. Marrying a commoner with awesome skills can be worth it, but those skills had better be good!
3. Fabricating a claim costs around 150 prestige, in addition to the gold required to bribe the locals to "remember" some facts about your claim.
4. A White Peace (if you're the aggressor) or surrendering a war will cost you some prestige, but you don't need to have prestige in those cases.

Though it's not an action, remember that you get an opinion bonus of +1 per 100 prestige, that applies to everyone. It caps at +20, but it's still quite useful!

I. Weak claimants can only press their claim under specific circumstances

• Regency
• Male claimant against female ruler
• There is already a war in progress disputing the title
• Claimant is currently a pretender (2nd or 3rd in line to inherit title)

II. Females cannot press claims against titles with agnatic succession laws.

So, when you see a claim that is not available as a CB

1. If the claimant is female, verify that the title succession law is agnatic-cognatic or absolute cognatic
2. If the claim is weak, verify that at least one of the specific circumstances apply
3. Male claimants with strong claims can always press their claims