Question

if someone is walking on a moving bus, name two reasonable reference points you might use to describe his or her motion

Answer 1

1st reference is the bus itself, for example the bus driver's seat as reference point. The 2nd reference can be the road outside of the bus, for example - the traffic lamp post as reference point. The 2nd reference is basically using the earth as reference. The 3rd reference can be the sun. Etc.

Answer 2

The best to describe their motion would be to the bus. This is because there is practically zero space between the person and the bus.
The Earth would be your second option. This is because there is a relatively small amount of space between the person and the Earth (say, a meter) and this will cause any calculation of velocity to be Slightly off. (and by slightly I mean a factor of 0.0000000000000000064 m/s off).