If you need to determine your WAC Server build, it is relatively easy.
Internet Explorer 11:
Hit F12 key (make sure the "F lock" key is selected). You will then see the below window.
1. Choose the "Network (Ctrl + 4)" icon.
2. Click the Play button "Enable network traffic capturing (F5)"
3. Click "Details"
4. Click "Response headers"
5. You will see the WAC build next to "MicrosoftSharePointTeamServices".
Internet Explorer 10:
In Internet Explorer (in this example IE10), browse to the location where documents are stored.
Hit F12 key (make sure the "F lock" key is selected). You will then see the below window.
1. Choose the "Network tab.
2. Click "Start Capturing"
3. Click "Details"
4. Click "Response headers"
5. You will see the WAC build next to "X-OfficeVersion".