Taking into account the Cgd of M1 and M2, you have a total of 3 zeros. Two high frequency zeros, z1=gm1/cgd1 and z2=gm2/cgd2. The other zero comes from the gain boosting amplifier. The pole at its output gn2*cn2 will be a zero in the main transfer function. gn2 is the conductance at node N2 and cn2 is the capacitance at node N2. This zero can affect your stability if you aren't careful about it.