Not possible from within the HyperspectralViewer app. However, you can achieve the same using the code below (just replace the spatial location row and column index with your intended ones).
% Read the hyperspectral image
hCube = hypercube("indian_pines.dat");
% Extract the DataCube adn wavelength
dataCube = hCube.DataCube;
wavelength = hCube.Wavelength;
% Extract the single spectral signature of the (50,50) spatial location
sig = dataCube(50,50,:);
sig = squeeze(sig);
% Plot the signature
figure
plot(wavelength,sig,"LineWidth",2)
axis tight
xlabel("Wavelength")
ylabel("Amplitude")
