Can I can get the Chinese Visa from Nepal? I´m Argentinean. How long does it tke to get it?

Hi, you can get it from Nepal. Since you already in Nepal and you want to visit Tibet, you are suggested to do it directly through a local tour agency.
Based on my information, the fee is 114USD per person. It takes around four working days to get it.
Since you will finally find a tour agency to help you to get a Tibet Travel Permit, so you had better ask them to help you to get a China Tourist L. It is much easier for them to get you one.