If a girl does not wear panties to a nightclub, then it says a lot. If she does this, then it is not just that, she probably pursues her own goals. And the goals are often very simple. In essence, this is an open demonstration of readiness for adventure, including sex for one night. If you are looking for the same thing as a girl without panties, then you can safely roll up to her.
If there is even a fleeting sympathy on her part, then everything suggests that you will have sex tonight. You don't have to invent something. If you can talk to this girl faster than the other guys in the club, then you have every chance.
You can use different strategies. From a simple guy who builds a regular conversation pattern, like “Hello! How are you? ”, to direct hints about sex. But to tell the truth, it is not so easy to notice a girl without panties. If you noticed this, then there is a high probability that the girl herself did it so that you noticed it. It is likely that the girl is giving you a hint, so go for it!