Below are the locations of the ConfigMgr 2012 R2 Client log files as a Task Sequence progresses from WinPE to the full version of Windows.
Windows PE before HDD format:
Windows PE after HDD format:
X:\smstslog\smsts.log and copied to C:\_SMSTaskSequence\Logs\Smstslog\smsts.log
Full Windows before SCCM Client:
Full Windows after SCCM Client is installed:
Full Windows after Task Sequence finishes: