I want to engage in a war (me and my big allies vs him and his big allies) and I'd like to see if any of his or my allies will skip the war because they're in debt. Is there any way to know this?
When calling your allies, you see if they wish to join or not, and when you check that, if you get the -50(?) penalty for "In Debt", then it sums it up. Not sure on opposing alliances.
Go to the Score comparison tab in the ledger and look at their admin score. If they have loans, they will show up there as a negative score modifier.
That doesn't really tell you anything, if they have 400 ducats and 0 inflation they could still have 10 loans of 500 each and have just spent points to lower their inflation.You can simply go to the "Countries" page (the first one?) of the ledger where each country is listed along with their income, current treasury and a bunch of other information.