I think I'm going to ask my ex about their finances.
Why would you question their finances?
They waste money.
It's good not to waste money, but their finances are none of your business. That is their personal life.
I can help them get their finances in order if they want to.
Don't you think you're overreaching boundaries with an ex? You two are no longer involved and their money is no longer your business and it can be imposing to them. How about using these skills towards your own finances and making your situation better?