A Toyota hybrid's 12v battery shouldn't be jumpstarting another car's battery. (Too easy to blow the fuse on your donor hybrid.)
The Toyota hybrid's 12v battery is smaller than an average car's 12v battery, because it never has to start an engine. So, if you do a traditional jumpstart/boost, you can overpower the hybrid's 12v battery, and potentially blow the fuse that charges it (from the hybrid battery).
The preferred method of jumpstarting another vehicle, using a Toyota hybrid is:
Turn off both cars.
Take the keys of the car to be jumped, so that the owner doesn't try to start their car on your donor hybrid's battery.
Connect up the jumper cables per the owner's manual of the car that needs to be jumped. It's probably best to go direct with your hybrid's 12v battery terminals, but if you have a NHW20 (2004 and newer) Prius (I don't know if the TCH or the THH have these jumpstart terminals...) you can probably use the under-hood jump points in the fuse box. Watch that polarity!
Turn on the hybrid to READY, so that the gasoline engine can charge the hybrid battery, the hybrid battery can charge the 12v battery, and the 12v battery can charge the dead car's battery. Leave like this for at least 15 minutes to recharge the dead car's battery.
Turn off the hybrid, and disconnect all the jumper cables.
Try starting the dead car using its own somewhat recharged battery.
Drive this car around for a while to let it recharge its own battery more.
This'll only work if the dead car's battery is merely too weak to start the car. If it has any damage or an internal short, it won't work (and could be dangerous to charge it).
The real preferred method, other than having an auto club (like AAA or Better World Club) come out, is to have a portable jumpstart kit for your car. Less than US$50, you can get a jumpstart kit that also has other neat stuff in it, like a compressor for tire inflation, or hazard lights. Something worth having in your car toolkit.
Jump start procedure if needing to jump your own Toyota hybrid if its 12v accessory battery is dead can be found in the "in case of emergency" section of the owner's manual.
In a traditional car, you'd have to drive around for a while after a jumpstart to get your 12v recharged, because the alternator is run off of the gasoline engine. In a Toyota hybrid, which doesn't have an alternator, you just have to leave the car in READY to charge the 12v battery off of the big hybrid traction battery. (But, if your car is on, you might as well drive it somewhere...) A good 30min drive somewhere should do the trick.