That Clojure 1.9 namespace qualified map syntax, it.e equivalent to {:selections :Prestado/:nm_usuario} (that is, the #: reader macro preprends the namespace to all keys in the map).

Is possible to access programatically ?

I'm aiming for relating this information with underlying table information to build a sql query

(comp namespace ffirst)

I'm not quite following you. This information is available inside a resolver function. Do what you want with it there, such as create a SQL query. If you need to extract data at this level but use it at a lower level, you can use the resolve/with-context modifier to pass context data to nested resolvers in the context.

I'm poking with the possibility of coding a generic resolver function to build a sql query. First step was extract that namespace. Thank you for the map information. I was not aware of it