how to display full stored procedure code?

use pgAdmin or use pg_proc to get the source of your stored procedures. pgAdmin does the same.

\ef <function_name> in psql. It will give the whole function with editable text.

SELECT prosrc FROM pg_proc WHERE proname = 'function_name';

This tells the function handler how to invoke the function. It might be the actual source code of the function for interpreted languages, a link symbol, a file name, or just about anything else, depending on the implementation language/call convention

\df+ <function_name> in psql.