What does a retired 2-star general earn for retirement?

It is a bit hard to say specifically. The normal retirement pay is based on salary at end of service, which in turn is based on rank and years of service. It will be between 50% and 75% of the base salary.

At 20 years (Generals are going to have more than 20 years, it is very unusual to achieve star rank in less than 20 years) you get 50%. You get an additional 2.5% for each additional year after 20 to a maximum of 75%. Based on the 2010 pay charts it would be between $75,516 and $79,314. That does not include full medical benefits and access to military exchanges.