In tools->; ; Options-> ; Environment->; ; Font and color. You can set it or use the default setting "Use Default".

Menu: Tools+Options+Text Editor+All Languages+General, and select the "Line Number" item in "Display".

If you only want to display or not display the line number of a specific language, you can set it like this:

Tools+Options+Text Editor+General, choose to display or not display.

This setting will override the global setting above.