Can't find kernel.log file on Yosemite
On Yosemite, those kernel messages should be logged to System.log according to /etc/asl.conf, which replaced the older syslog.conf. Apple System Logger and Syslog both use /etc/asl.conf

 # Rules for /var/log/system.log 
 &gt; system.log mode=0640 format=bsd rotate=seq compress file_max=5M all_max=50M
 ? [= Sender kernel] file system.log


Kernel.log is not used by any logger since 10.8 I believe, but confirmed in 10.10.x

Note, El Capitan and SIP removed support for kext-dev-mode, so keep that in mind if you need to debug in newer OS X versions.