I want to know the number of rotor poles. Can i use the following method? I mark the start point. I slowly rotate and note the Hall changes and see how many times the hall code repeats when it comes back to original position. Is it correct method?

 

Short the three stator wires and rotate the shaft by hand and count the 'bumps' per one rotation!
Max.

 

I tried but seems to be little difficult. I can't figure out the total number of bumps. It is confusing.

 

Usually it is quite evident. But alternatively you can monitor one of the Hall outputs with a meter.
The PDF shows the corresponding BEMF of the windings, for this display on a D.B. scope, you need to set up a virtual neutral, wire a 10k res to each phase and connect all three ends together and make this scope GND.
Rotate at a low rpm
Max.