If the unfinished sentence 'She knew that' is leading into another clause, it should be followed by an ellipsis or a dash to indicate the trailing off or pause in thought. The exact punctuation would ultimately depend on how the sentence continues.
When considering the unfinished sentence 'She knew that', there is no clear ending, which implies that the sentence is a fragment and requires additional information. If the sentence were to be completed, the appropriate punctuation would depend on the context and continuation of the sentence.
However, since it is incomplete and likely intended to be followed by a clause explaining what she knew, the most appropriate punctuation to follow would be an ellipsis ("...") to indicate that the sentence trails off or is unfinished. Alternatively, if the sentence is intentionally being left open and suggestive, a dash ("-") might be used to imply an abrupt pause or an unfinished thought. In dialogue or narrative, it could also end in a period (".") or comma (","), depending on how the next part of the conversation or sentence is structured.
The probable question may be:
"What all the punctuation would you use after this sentence?:
She knew that __ (some statement)"