I recommend changing the comma after Wait to a period and starring a new sentence with So, but that isn’t absolutely necessary.
There’s a dot missing from the ellipsis before the question mark. (No, you shouldn’t leave one dot out just because there’s another punctuation mark afterward.)
Also, She trailed off… isn’t a dialogue tag; it’s an associated action (sometimes called a beat, which is confusing because some people call everything other than actual spoken words during a conversation beats). Write it as a separate sentence. (If you want it to be part of the same sentence, write it this way: “Wait. So if this isn’t the poison… where is it…?” she said, trailing off as she looked at the glass from which they’d all just drank.)
“Wait. So if this isn’t the poison… where is it…?” She trailed off as she looked at the glass from which they’d all just drank.