How do I list all columns for a specified table

In addition to the command line \d+ <table_name> you already found, you could also use the Information Schema to look up the column data, using information_schema.columns:

SELECT *
  FROM information_schema.columns
 WHERE table_schema = 'your_schema'
   AND table_name   = 'your_table'
     ;

Note: As per the example above, make sure the values are enclosed within quotes.

As a supplement to the other answers, even a SELECT statement that returns no rows will expose the column names to you and to application code.

select *
from table_name
where false;

Permissions might come into play with any of these approaches.

The information schema is the slow and sure way: it is standardized and largely portable to other databases that support it. And it will keep working across major versions.

However, views in the information schema often join many tables from the system catalogs to meet a strictly standardized format - many of which are just dead freight most of the time. This makes them slow.
The Postgres developers aren't making promises, but basics (like what is needed here) aren't going to change across major versions.

psql (the native command-line interface) takes the fast lane, of course, and queries the source directly. If you start psql with the parameter -E, the SQL behind backslash commands like \d is displayed. Or \set ECHO_HIDDEN on from the psql command line. Starting from there you can build an answer to your question.

Given one table, is it possible to have a list of the names of the columns for this table.

SELECT attrelid::regclass AS tbl
     , attname            AS col
     , atttypid::regtype  AS datatype
       -- more attributes?
FROM   pg_attribute
WHERE  attrelid = 'myschema.mytable'::regclass  -- table name, optionally schema-qualified
AND    attnum > 0
AND    NOT attisdropped
ORDER  BY attnum;

Faster than querying information_schema.columns. Try EXPLAIN ANALYZE to see for yourself. Still hardly matters for a one-time look-up. But might make a difference if used in a query / function that's repeated many times.

There are also subtle differences in visibility. Detailed comparison:

• How to check if a table exists in a given schema