Using METAbolt it is easy to get the UUID of anything you require:
Logged in avatar
Upon log-in the UUID will be printed at the top of the chat screen. You can also go into the profile of the avatar and find that it is printed at the top of the profile screen.
Other avatars
Select the avatar from the radar list and click on the profile icon on the right (radar toolbar). You will then see the UUID at the top of the profile screen.
Inventory folders
Select the folder you need and click on the "Changer" icon at the top. The name and the UUID of the selected folder will appear on the right hand panel.
Inventory items
Click on the inventory item and both the asset and item UUID will be displayed on the right hand panel.
Objects
Go into the Object Manager from the Tools menu option and select the object you need. The UUID will be displayed on the right hand side of the window.
Groups
Select the group you want from the Groups tab and click on the Info button at the bottom. The group UUID will be displayed at the top of the Group Information window.
Group Roles
On the group information window click on the "Members & Roles" tab, then on the "Roles" tab. You will see the UUID of each role next to them.