What is magnetization resistance and how to calculate(or measure, or estimate) it?
The magnetizing resistance is the Rm and is used to model the no-load losses in the classic equivalent circuit of the transformer. To calculate you need to know the no-load losses and the voltage of the primary (there is a detail on which side to position the magnetizing branch, in your figure, it is in the primary winding, numbered as 1). You can use:
$$Rm=V_1^2/P_0$$.