Yes, I also agree that the objectives should always be SMART. They also need to be clearly stated before the task begins to prevent any confusion. If he agrees to give you a chance each time to ask questions before you start a task this may help. This could be a set command you can follow 'i.e. 'You may ask any questions/speak freely etc) or it could be that you have the right to ask permission to speak and ask questions without fear of reprisal. This way you can ask questions and voice objections without violating the TPE set up as it is intrinsic in your contract with him that, at certain times, you may speak.

Of course, you should never be able to refuse a task outright but he may be inclined to offer you an alternative or modify a task based on your questions or objections.

I think it is also important that this 'question time' be respected as a time when no reprisals are possible from him to you so that you can speak freely without fear. However, you will need to learn to use this time wisely and not over use the privilege.

The ability to set effective tasks is something that comes with practise, it is not something that can be wholly taught. Experience will make him better at it and it is good that he seems willing to learn and involve you in the process.