I've put some printk()'s in some of the filesystem files of the linux source tree to try and trace what's going on.
When I run dmesg, I can see a few of my traces, however they aren't showing as I would have expected when I then call the functions again via the terminal.

How can I call some of the system calls and see a modified output?

Just gonna answer my own question in-case anyone else is looking for it.

printk() at the default level, outputs to the /var/log/messages file

printk("I am at default level");

The printk level can be defined however to the following levels.
KERN_EMERG
KERN_ALERT
KERN_CRIT
KERN_ERR
KERN_WARNING
KERN_NOTICE
KERN_INFO
KERN_DEBUG

printk(KERN_CRIT "I am a critical level printk");

If it's critical or above, it will print in the terminal as well as /var/log/messages