How do you know when the dbq is ccot, causation, or similarities/differences?
That really depends on the prompt and the documents. It will change depending on what is given to you. Some essays lend themselves better to causation then comparison. Sorry for the non-answer but go with your gut!
Look for the verb given by the prompt:
CCOT: persisted, changed
Causation: caused, affected, impacted, transformed
Similarities/Difference: “two or more ____”