@User from the terminal where you launched xschem from, or you can add an 'action' object on the schematic and trigger the annotate command by clicking it. However please wait, it's not a push button operation, you need to place some monitors about the things you want to see in the schematic. You can examine the 'mos_power_ampli.sch' schematic that is included in the xschem examples/ directory. Will write a comprehensive tutorial.