Apple - Activity Monitor columns missing
You can refresh your Activity Monitor settings by deleting the preferences file, and then re-opening the app.
Open Terminal and paste in the following command:
Hit enter, and reopen Activity monitor - the columns should now be present.
The "Process Name" column is too big, causing it to crowd out the other columns pushing them to the right side. You can manually resize the "Process Name" column by enlarging the Activity Monitor window, scrolling far to the right, and then dragging the column separator between "Process Name" and the next column back to the left so that the column is standard size again.
This problem happened to me after a Catalina update. For whatever reason, the default size of that column was changed by the update causing this to occur.