Review the item:
When Robert is riding his motorcycle, he drives recklessly, weaving dangerously
through rush hour traffic, Robert does not care that
he might leave a kneecap or chunk of thigh speared on a car bumper.
No punctuation of any kind is necessary between care and that. Robert does not care is a main clause. That he might leave a kneecap ... begins a subordinate clause that must be attached to a main clause.
Generally, when a subordinate clause follows a main clause, as in the example above, you need no punctuation between them.