Sites on a Tree shows a phylogenetic tree for a protein family along with the sites you choose (example). Or, it can show all the known functional residues (example).
The first step is to search for characterized homologs of your sequence, or to upload your sequences.
Or upload unaligned protein sequences in fasta format. Limited to 200 sequences.
Or try SitesBLAST: find homologs with known functional residues and see if they are conserved
Lawrence Berkeley National Laboratory