Ask (for)

When you're making a request using ask, the following are possible:

• I'll ask the waiter.
• ask someone
• I'll ask the waiter for the menu.
• ask someone for something
• I'll ask the waiter about the menu.
• ask someone about something / someone
• I'll ask the waiter to bring us the menu.
• ask someone to do something
• I'll ask for the menu.
• ask for something / someone
  (the structure most likely to be used by a native speaker)

Notice that ask something is not in this list. The picture below shows a woman asking something for information.

a woman 'asking the menu'