Where do we learn Tom Robinson is in Ch. 23 and what is Atticus's plan for him

Tom Robinson is in another prison seventy miles away.

Atticus believes that his appeal has a good chance.

Explanation:

In the discussion between Atticus, Jem and Scout in the house of Atticus on the behaviour of Bob Ewell, we learn that Tom Robinson is sent to another prison. In the same discussion Atticus states that his appeal has a good chance and, while speaking of the jury trial, confirms this by saying:

'A white man's word always beats a black man's word'