Once again, compare the default templates i.e. try admin using the default theme and you will see how it should look.
There are a large number of changes, so picking out those specific to sub-forums is not an option - something like WinMerge is the best way to highlight changes between default and custom themes.
You will eventually have to do it anyway - 9.3.x and 10.x CVS versions also have sub-forums.