Hiya!
You have a couple of options.
You should be able to use the validateJWT method on the fusionauth node client. That calls this API: https://fusionauth.io/docs/v1/tech/apis/jwt#validate-a-jwt
You can call into /oauth2/introspect, but you'll have to construct that URL manually, as it isn't currently supported by the client libraries.
Finally, you can also use a jwt package (like this one) to verify the JWT is still valid without communicating with FusionAuth.
Hope this helps.