In SCCM 2012, CMTrace.exe will replace the well known log viewer Trace32.exe. And now it’s an integrated part of the installation. On the first start of CMTrace, it will ask you, if this log viewer should be the default viewer for .log files.
On the server you will find the tool here: [SCCM2012InstallationPath]\Tools\CMTrace.exe.
And the viewer is also available while OSD (Operating System Deployment). In this case, the path for x64 is:
[BootDiskDrive; usually x:]\sms\bin\x64\cmtrace.exe
And for x86 it is:
[BootDiskDrive; usually x:]\sms\bin\i386\cmtrace.exe