After hours and hours, finally got it like so:
const args = `
{
set {
_:blank-0 <Post.name> "${args.name}" .
_:blank-0 <Post.description> "${args.description}" .
_:blank-0 <Post.published> "${args.published}" .
_:blank-0 <dgraph.type> "Post" .
}
}
`;
Note: dql requires the newlines, unlike graphql.
const results = await dql.mutate(args);