all words show the potential or possiblity that is janu " to know "( potential is there that is you might know the thing ) and similar word janunga " i will know ".( potential is there that in future you will know about that thing ) similarly karu (karunga) ( likey to do ) { possiblity or potential that you will be doing that ) and mangu ( manguga) ( i will ask for it ) ( again it show possiblity that you will ask for something ) janu , karu, mangu you can think.them as the short form of these words manguga , karunga,janunga ( these are bit polite to say also )

Janu - to know Karu - to do Mangu - to ask for However these are not the correct words. I would consider it to be the the ruined version of Hindi The correct ones are Jaan (जान) Kar (कर) Mang (माँग )