Please help me...I read all about wonders in rulebook and i dont understand what is the purpose of obsolete a wonder... What I earn? I may build another wonder in that city? Why would I obsolete a wonder?
You do not obsolete them. Other players do it to you. When a wonder becomes obsolete it no longer has any abilities, but it still provides the culture tokens.
You can build over an old wonder even if it is not obsolete.