If you want to know the exact amount of damage a weapon is dealing to an enemy in Starfield, then you can check out this Seeking Tech guide to see how you can get the game to show damage numbers.
1. To start off, go to the Settings menu from either the main menu or pause menu in the game.
If you are playing on Xbox or with an Xbox controller, then you have to press the Menu button while you are in the pause menu.
2. From Settings, you need to select Interface from the list of options.
3. Inside the Interface section, move the cursor down to Show Damage Numbers. This should show the following information on the right side of the screen:
Enables showing floating damage numbers on the HUD.
4. By default, Show Damage Numbers is set to Off. You will need to select it in order to toggle the option to On.
5. Afterwards, exit the Settings menu of Starfield.
The next time you deal damage to an enemy, you should see the damage numbers appear on the screen.