What is the PDF for path tracing in the paper "Learning the light transport the reinforced way
I have to answer my question. 
Consider that all patches have the same value. Then choosing a patch uniformly and selecting a random point uniformly on that patch is as the same as sampling the hemisphere uniformly. If $p_s=Pr(Q_k \in Q)=1/n$, which n is the number of patches, I can conclude that $p_\omega=p_s*(n/2\pi)=1/2\pi$ .

And if patches don't have the same value, then $p_s=Pr(Q_k \in Q)=q_k/(q_1+...+q_n)$ and 
$p_\omega=p_s*(n/2\pi)=(q_k/(q_1+...+q_n))*(n/2\pi)$