In an ISA (ICAO Sstandard Atmosphere), the tropopause is between 35,000 and 36,000 feet. It is usually defined as the level of maximum wind. At the trop, the temperature should also stop decreasing. Close to the equator (up to +/- 23.5 degrees depending on season) the trop is at its highest height; close to the poles, at its lowest.
Normally CB tops don't exceed the tropopause. However, during periods of extreme vertical activity, the tops may exceed the trop quite dramatically.
I have seen CB tops in excess of 70,000 feet in the south Pacific; and tops in excess of 50,000 feet in Alberta!
Volcanic plumes can also well exceed the trop.