How to simulation different kinds of Noises in speech signal?
Types of noises which you could try, that come to my mind at this time are:


White noise,
pink noise,
impulsive noise,
babble(multiple persons speaking in the background)


You can generate white(awgn)/pink noise(pass the white noise through a filter) in matlab.
You could record impulsive noises(pen clicks, knocks on the table, etc), and babble(record yourself and or others multiple times and overlap the recordings)