To find this cache you will need to know your ABCs and be able to input a keyword into Certitude. The keyword in particular is nothing more than a letter of the English alphabet
You should hopefully know there are 26 letters of the alphabet, so worst case is you could potentially put in each and every one until you potentially stumble across the solution. If you pay close enough attention to all details on the page, they may narrow it down for you. Good luck!
You can validate your puzzle solution with certitude.