Dear @couet
Thank you very much for your response. Here’s the solution. It might not be straight forward to guess the names of the PDFs.
TLegend *leg = new TLegend(0.57,0.73,0.78,0.93);
leg->SetBorderSize(0); // no border
leg->SetFillStyle(0);
leg->AddEntry("h_data","Data","pe");
leg->AddEntry("pdf_Norm[deltaM_kspipi]","Total Fit","l");
leg->AddEntry("pdf_Norm[deltaM_kspipi]_Comp[gauss]","Gaussian","l");
leg->AddEntry("pdf_Norm[deltaM_kspipi]_Comp[johnson]","Johnson","l");
leg->Draw();
Here’s what helped.