when to use "ki" and when to use "kii" in a sentence ? i mean when to use it with choti "e" ki matra and when with badi "e" ki matra ?

 I too used to get confused.  Choti ki is used for continuing a sentence like

neha ne bola ki........ and badi ki is used when a thing is someone's like 

yah neha kii kitabh hai. 

Ki is used when we are using it in place of THAT and otherwise it is kii

For example, Ram kii cycle toot gayi (ram's cycle's broken)

                    Ram ne kaha ki tum mat jao (Ram said THAT you don't go)

If this helps then please gimme a thumbs up!!