Adding PageUp/PageDown to a keyboard without

I have a laptop with an english mapped keyboard that has not the PageUp/PageDown keys.

How could I add these keys also with a combination?

I am using gnome.

What’s the make and model of the keyboard?

Teclast F5

Have you tried Fn+ :arrow_up: / :arrow_down: ?

Yes, tried but the result is :arrow_up: (and down) as the Fn was not pressed.

You should be able to use xbindkeys to map the keys.