Hi Diana and welcome,
(Note: I fixed the [s ] notation in your post, because the forum tries to use that for strikethrough text if there's no space in it.)
First, note that -s can be used for either plural nouns (cats) or for third-person singular present-tense verbs (goes). That's just coincidental and the two usages are completely unrelated but oddly enough for phonology the effects are identical so it doesn't really matter which one you look at (or even both at the same time). Here I think you're mostly looking at the third-person singular present-tense verbs though. (If you want an abbreviation for that it's usually just "3SG".)
bash [ˈbæʃɪz ] [ˈbæʃd]
stink [stɪŋks ][ stɪŋkd]
Those look fine for the first part and most of the word. But take another look at the -d at the end of the last two. Don't be confused by spelling! Do you actually say [d] or do you say [t]?
Are you a native speaker of English? If you're not, then I suggest trying to find a recording of some of these words to check or asking a native speaker. Your observations will probably be fairly reliable, but your intuitions might not be, so questions like this can be challenging.
If you are a native speaker, that will help, but it can also confuse you: due to what is called "categorical perception" you won't actually hear these subtle differences because it's roughly "one sound" (a phoneme) in your head, or perhaps you think of it as a letter like "d". "It's just a D right?" Actually, no. But we hear it that way (which is useful for understanding the meaning.)
A really interesting activity (if you have the time) is to separate recordings into individual sounds. You'll be surprised how different they sound in isolation-- without the context you'll be more likely to pick up on some differences.
Alright, so that's enough background info, on to your main question--
However, I am not finding a pattern between the words using [s ], [z], [t], and [d].
Could anyone potentially give me a clue as to what I should be looking for?
Given that this is homework, I want to help you rather than give you the answer.
Look at the following nouns (remember, it's the same -s sound as above). What's going on with the plurals?
cat cats
dog dogs
Do those sound exactly the same?
Think about 'creative' spellings of the plurals. Which one of these is more natural?
catz / dogz?
It turns out that the "S" in those two is actually pronounced quite differently.
If you can just remember that pair then the whole thing should start to make sense.
I've already probably given away too much, but as a last hint: look up
voicing in your textbook.
