If i modify something Host profile and want to see the same is reflected in host in the logs.
which log & directory i need to look for ??
look in the host's /var/log/syslog.log file . you will get the detailed logs there.
Here is a nice vmware blog which can help you out. Tips for Troubleshooting Host Profiles | VMware vSphere Blog - VMware Blogs
If we do the configuration in the host profile then its may be capture in INFO log in syslog log. Is there any specific log for host profile related.
Except this all the logs are captured in to the vcenter logs. You need to revisit your vcenter logs to check for your host profile events and logs.