If you are working with multiple aligned protein sequences you can see the percentage identity and similarity values for the active sequence window in the bottom-left corner of the Discovery Studio interface. If nothing is selected, all of the sequences are considered. If only certain sequences (or fragments of aligned sequences) are selected, the reported percentages are for the selection only.

A quick way to see the similarity for the same aligned residues is to select the desired residues in one sequence, right-click in the sequence window and choose Extend Aligned Selection. This will select the aligned residues across all the sequences and the bottom-left of the interface will show the percentages for those aligned residues.