1 : ''which book r u talking ?'' they wanted to know 

=> they wanted to know which book i was talking 

2 : she wants to speak english perfectly, so she practices evry day

=> if she practices speaking english every day, she can speak it fliently

3 : work hard and he'll pass his exam

=> if he work hard, he will pass his exam

4 : ''dont wipe ur dirty fingers on my nice clean table cloth'' she asked him

=> she asked him not to wipe his dirty fingers on her nice clean table cloth

1. they wanted to know which book I was taking

2.If she practice every day, she can speak English perfectly

3.If he works hard, he will pass his exam

4.She asked him not to wipe  his dirty fingers on her nice clean table cloth

công thức: 

S+asked+if/wether+S+V 

If + S + (don’t/doesn’t) + V(hiện tại đơn), S + will/won’t (be) + V +…