I'm trying to find a way to implement SHACL validations using SPARQL in my AWS Neptune Graph database. Is there a way to do so?
Well, it depends on what you mean by "implement". ;-)
You cannot implement all of SHACL with SPARQL alone, but you could implement some subset; not with a single query, though. You could, for example, write a query that collects the constraints of your shapes, and then use those results to generate a query that gets the relevant parts of your data; you could then examine those results and produce a validation report. And if you are doing stuff programmatically, you could of course implement also those parts with cannot be expressed through SPARQL (e.g., literal string patterns).
All that is somewhat "academic". There are open source SHACL implementations that you could use as a Neptune client (e.g., pySHACL if you are using Python and RDFLib). That would be a better and certainly a far more practical way.