plotwithLabel = Plot[x, {x, 1, 2}, PlotLabel -> "This is Label"];
PlotLabel /. Cases[plotwithLabel, _Rule, All]
"This is Label"
plotwithLabel = Plot[x, {x, 1, 2}, PlotLabel -> "This is Label"];
PlotLabel /. Cases[plotwithLabel, _Rule, All]
"This is Label"