This can be a difficult one to get, I definitely struggled until I watched this video, courtesy of Geoff & Jack over at Rooster Teeth.
The 11 Monitors are located in 10 chambers. Although they are found in 10 chambers in sequence the chambers the monitors are found in are labelled as follows-
1 (not Wheatley's push the button chamber), 2, 3, 4, 5 (2 monitor's in here), 6, 11, 12, 15 & 16.
Make sure you save at the beginning of each chamber