It depends on what the computer is being used for. For general typing of letters of essays, "Space" or "e" are probably the most used. For a gaming computer "w" (walking forward in most games) is often the most used key by a large margin, followed by "a", "s", and "d" (left, backwards, and right is the WASD control setup). Computers that run other specific programs a lot might have another key, such as "Enter" that is used the most because it is associated with a specific function.
If you right-click on the mouse or hit the shortcut menu key on your keyboard, a menu appears with common commands that are used or are relevant at the time depending on what you are doing. This menu is known as a shortcut menu.
At right side of the keyboard there are shortcut keys. They are are used by right fingers.
There isn't default keyboard shortcut to link layers but you can assign shortcut from Edit > Keyboard Shortcuts.
Qwerty is the most common keyboard layout
The most common keyboard used nower days is a Qwerty keyboard.
shortcut key
Because some people prefer using the keyboard instead of the mouse.
Ctrl + V
Alt + enter
it is laptop
Windows logo key + E
Ctrl plus J is used to justify text or a paragraph.