Likelihood on simultaneous fit


I would like to plot the likelihood of variables coming out from my simultaneous fit.
I don’t understand which dataset and pdf I have to consider.

I know:
RooNLLVar nll(“nll”,“nll”,pdf,Data,kTRUE);

but I have the background and the signal plotted simultaneously, with two different pdf.
Which pdf and data I have to put here in order to see the likelihood plots of signal variables?