how do you know what kind of expense falls under each tax line
how do you know what kind of expense falls under each tax line
how do you know what kind of expense falls under each tax line

If you can get a copy of the tax form, such as a Schedule C for a sole-proprietor, you will have the major expense items. If you have an expense item that does not fit in any particular line category on the tax form, you might want to ask your accountant as to the best category to put it in. I hope this helps. If not keep asking questions or mark this as solved.

this "feature" has wisely been discuntinued in newer versions of QB
its use was generally misleading leading to false and incorrect tax reporting by non-accountants attempting to use it, since bookkeeping data generally never corresponds to income tax treatment for all transactions in an enterprise
recommend using proper tax procedures (by accountant) and not attempting using this in bookkeeping software like QB