how do i know a substance is an acid or base without litmus paper

Answer 1

In the olden days, you could taste it, can't advise that anymore. Some acids you can smell (acetic, hydrochloric, nitric, sulfuric). You can drop a small piece of chalk in it, if acid, it bubbles. Some bases smell also, ammonia is a common one at my house.
So the answer to your question: You have to have experience on what to detect, and how to do that, and be careful. This is why I always taught the final essential step in diluting chemicals: Label that which you prepared immediately, not putting if off.