In a Google-Sheet called Field Schedules for Google web-apps at http://drive.google.com you can right click on a cell to open a context menu with the option to "Insert comment." Let's say for example I insert a comment: "hello world." into the cell "A1."
After I create comments, I attempt to open the same Google-Sheet, Field Schedules on my Boss's iPad, or on my LG-G2-Android device and I do not see any option to "Insert comment[s]." Nor can I find comments that already exist.
After exiting the Field Schedules from the Android & Apple devices I can confirm that the original comment exists by using my desktop computer to open Field Schedules and hovering my cursor over "A1" it will then display my comment "hello world."