Excel will display the Chart Element Names when you hover over on chart's different elements, but if accidentally hide Chart Element Names on your computer and you want it back, please follow the steps below:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left navigation menu in the dialog box;
Step 4: Check "Show chart element names on hover" under the section of "Chart";
Step 5: Click "OK" at the bottom to apply the changes.