image rejection ratio

For any system level design, at which point we have to calculate the image rejection ratio?

Is that at the final output i.e., after Amplifire or can calculate after any subsystem?

Image rejection ratio is the power ratio of image signal before down-convertion (RF) and after down-convertion (IF). So you should calculate the IMRR at the mixer output. But if polyphase filter is used for image rejection, calculate the IMRR at the polyphase filter output.

After the filter usually. which is the most important component for rejection.

So I think you can test it after the system.