Honestly Ljubljana really isn't big party city. I hardly recomend you something ... it also depends what kind of people you are ... if you are students then club like KMŠ will be cool for you. If not then some more "fancy" clubs like Circus, TOP will be cool for you. But my advice would be Metlekova mesto. It's an autonomous social centre. There are a lot of clubs, bars, concerts etc. Very unique place actually. More underground scene but usually very interesting for foreign people (my ex German roommate was really exicted about it.