Where would you find ULS logs on Office Web Apps (OWA) 2013 server
For my own record as well: C:\ProgramData\Microsoft\OfficeWebApps\Data\Logs\ULS
If you do not see C:\ProgramData folder, you need to change your explorer's viewing option to "Show hidden files, folders and drives".
Enjoy troubleshooting OWA!
Zewei Song, Ph.D.
Microsoft Certified Master: SharePoint 2010
Microsoft Consulting Services