This is measured by showing relevant evidence during interrogations and when you are trying to earn a warrant. Remember to save before an interrogation/warrant and then find the correct evidence, then reload the save and then get it right the first time.
These achievements do stack so getting 100% cunning will get you Fool Me Once and Can't Get Fooled Again achievements, as well. To check your cunning percentage, click on the PDA, and then go onto case file, and then go on statistics.
Use this guide to get this achievement easily on case 2: Guide