
Aratrok |

If the DC of the check is 10 or less (which would apply for CR 1/2 or less creatures, or creatures up to CR 5 that qualify as "common") you can make the check without any ranks.
Knowledge wrote:
Training You cannot make an untrained Knowledge check with a DC higher than 10.
Knowledge wrote:
You can use this skill to identify monsters and their special powers or vulnerabilities. In general, the DC of such a check equals 10 + the monster’s CR. For common monsters, such as goblins, the DC of this check equals 5 + the monster’s CR. For particularly rare monsters, such as the tarrasque, the DC of this check equals 15 + the monster’s CR or more.