He will say that he interpreted the requests in a way that led him to believe Trump wanted him to prematurely close the investigation but no way he will use the phrase "obstructed justice" or anything similar. Also he will respond with the "can't comment on an ongoing investigation", "I don't feel it's appropriate", and "answering that question may cause me to reveal classified information" on many of the hot button questions.
My sense is that he's only publicly testifying to get his interpretation of the meetings out there as that relates most directly to his personal handling of the investigation. Comey is a "good guy" and wants Trump gone but if he could've accomplished that while keeping the public in the dark about all of the details he would have. Remember he is an institutionalist.