Electric field of point charge 
in above picture, we have two point charge ( same size ).
Does electric field of q2 at location of q1 depend on size of q1?
because we know when we want to measure electric field of a charge, use another test charge which it is very small.but two charge have same size here.
 A: No it doesn't. The electric field at a point is defined as $$\vec E=\frac{1}{q} \vec F$$ in which $\vec F$ is the force on the test charge q placed at that point. The force $\vec F$ is itself proportional to q, so the division by q makes the field strength $\vec E$ independent of q.
Ideally we define $\vec E$ as the limit as q approaches zero of $\frac{1}{q} \vec F$. The reason for doing this is so that the test charge q doesn't alter (by attraction or repulsion) the positions of the 'source charges' whose field it is supposed to be measuring. If, in your case, the source charge, q2, is firmly fixed it doesn't matter if the test charge isn't approaching zero. 
A: Each charge generates its own electric field. The total field is obtained by adding up the contributions of all charges. This is a consequence of the linearity of Maxwell's equations.
So no, the field generated by $q_2$ alone is oblivious to the presence of other charges. The total field however is the sum of the fields produced by both charges. Note that the field is not defined at the exact position of a point charge though. The Coulomb potential diverges at these points.
However, since a charge does not exert a force onto itself, charge $q_2$ feels the electric field from charge $q_1$ alone.
A: I think you misunderstand about size you take it on a wrong way ,size means magnitude of a charge and  it is govern by formula Q=ne (number of electron ) and secondly he test charge is taken in small magnitude q so that it doesnt effect charge distribution of source charge .
A: The electric field is defined as the force per unit charge. It is best to use a small test charge in order to avoid secondary effects on your measurement due to the field of the test charge, but on principle it is independent of the amount of test charge. 
