This is a good question! We say many words in spoken English that seem to not carry much meaning. It can be very confusing, right?! (just an example). However, they can have a subtle meaning, like in the examples you gave.
"Though" (easily interchangeable with "although" which is more formal) is an adverb that expresses contrast or a change in position between two ideas. Let's look at your examples:
"His denim jacket, though." This might be spoken if someone usually feels like the person is a good dresser, but they really don't like his/her denim jacket. Though, it could also mean that they feel the denim jacket is really cool when compared to something else about the person. You will need more context or information to determine the speaker's meaning.
"For real, though." In my experience, I hear this when people are joking, exaggerating, or saying something that might not seem true. When they say "for real, though," they are saying that they really mean that it is true. Although, people may say this to emphasize their joke. Context is always important.
"When are you coming over, though?", "What's up, though?", and "really, though". These examples seem a little different than the others. This seems like an unconventional way of changing or focusing the subject.
I hope that this clears things up for you. Remember that spoken language doesn't always follow grammatical rules. Most of the time, as long as you understand the meaning of the person speaking, the grammar is usually unimportant. It's a fun question, though ;)
Feel free to contact me if you have any additional questions!