Senteria: Basically hold down crtl to bring up the menu and hover your cursor over to select the bomb (you want) by clicking on it.
And then...?
I'm playing with controller, because stubborn Geralt won't walk when I click on the mouse and WASD is no go. But. There are some things I can't figure out with the controller, because there's neither anything about it in the manual, nor in the in game tutorials. Like I need to switch to MKB to play dice or play without rerolls, because the displayed button just ends my turn.
Same with bombs: I can select them, but how do I throw them? How do I aim?