Lot of us, already have used OCS Logging Tool.
OCS Logging is used to collect log through the server. But, if you have a farm of Lync/Skype you need to know where is the user or run in all the servers before to reproduce the error.
So, to simplify, in Lync Server 2013/Skype for Business Server 2015, there is the Lync/Skype for Business Server Centralized Logging Service Agent. Then, you need to collect just in one server of the target pool. To check which scenario exists, run Get-CsClsScenario | Select-Object Name
After choice the better scenario, you need to start and reproduce the error.
Start-CsClsLogging -Scenario <name-of-scenario> -Verbose
Stop-CsClsLogging -Scenario <name-of-scenario> -Pools <name-of-the-pool>
Sync-CsClsLogging -Pools <name-of-the-pool>
Search-CsClsLogging -OutputFilePath “fullpath\clslogging.txt” -Verbose
Here, you can find the corresponding scenario with Logging Tool