How to write i hat and j jat from keyboard in ubuntu 18.04? [duplicate]

In this educational resource there is a complete list of symbols arranged in alphabetical order.

The simplest way I have found to use them is to copy and paste from the resource.

Try using the keyboard layout of a language that actually uses hats, like French, for example (hats are called accents circonflexes).

Check the steps here https://askubuntu.com/a/1030433/1066357 on how to add and select a language, and assign a keyboard shortcut to switch keyboard layout. You can add any variant of French.

Then you just have to switch to French layout using the settings or the keyboard shortcut, type ^ (the key immediately to the right of P, see below) then j.