Showing that the dual space of $H^{s,p}(\mathbb{R}^n) $ is $H^{-s,p'}(\mathbb{R}^n)$ with $\frac{1}{p}+\frac{1}{p'}=1$

Question

The dual space of $H^{s,p}(\mathbb{R}^n)$ can be isometrically as the space $H^{-s,p'}(\mathbb{R}^n)$ by the duality pairing $<u,v>_{H^{-s,p'}\times H^{s,p}}=<J_{-s}u,J_{s}v>_{L^{p'}\times L^{p}}$? ($J_{s}$ bessel operator)

Given the theorem of the previous image, how can I prove that this dual pairing is not degenerate?since I don't know how to interpret that internal product ... Example: $<f,g>_{L^2\times L^2}:=\int f(x)\overline{g(x)}dx$ but $<f,g>_{L^{p'}\times L^p}:=¿?$