You should not be dealing with node ids. They are deprecated, and will go away more and more.
To retrieve the labels, copying straight from https://github.com/Readify/Neo4jClient/wiki/cypher-examples, this Cypher:
MATCH (user:User)
WHERE user.Id = 1234
RETURN labels(user)
Is this C#:
graphClient.Cypher
.Match("(user:User)")
.Where((User user) => user.Id == 1234)
.Return(user => user.Labels())
.Results