1. What do you like most (or least) about your current job?
Regardless of whether this question is asked of you in a positive "like most" or negative "like least" way, keep one fact in mind: you are being asked a projective question. This means simply that your interviewer will take the answer to what you liked least or most in your present job and assume that's what you'd like least or most in the job he or she might offer you. So while you want to be truthful in responding to the question, you don't want to wave a red flag in front of your interviewer's face by saying that you hated some aspect of your job that might well be incorporated into the job you are interviewing for, or that you love some aspect of your present job that's unlikely to be part of the one you are trying to get.
In a situation like this, you're best off to let your interviewer know that there is no one thing you like best about your present job, but rather there are lots of aspects you truly enjoy. And, if at all possible, try to avoid answering this question until you have a good understanding of the job you are applying for. Then, when you do answer this question, tell your interviewer about the things in your present job that you have already discovered are important aspects of the job you're applying for.
For example, if you enjoy planning and controlling projects and you suspect that the job you are applying for involves a lot of both, you sure ought to mention this. On the other hand, if you have learned early in your interview that the job you're applying for involves planning only and no control, you'll take yourself out of consideration if you mention you enjoy both. So your best bet is just to mention how much you enjoy planning.
In responding to the negative version of this question (liked least), you are urged to dislike as few things as possible! Nobody wants to hire a person who sees too many minuses in any job. If you feel you must reveal anything you don't like about your present job, let it be what your interviewer would expect to hear. For example, if your kind of work involves too much travel at certain times of the year, let your interviewer know that "excessive travel is something you don't care for, but have learned to accept as part of this kind of work." And always keep in mind that the more you learn about the job you are applying for prior to fielding questions like this, the better you'll be at answering them.
2. What is the toughest thing you've had to handle in your present job?
This is another projective question. Your interviewer assumes that the toughest thing for you in your present job is likely to be the toughest thing in the job you are interviewing for. It goes without saying that your answer should be truthful. At the same time, be fair to yourself. Consider the A student who finds calculus toughest and gets a B+ in it. Then contrast this student with the C student who gets an F in calculus. One person's "toughest" is not necessarily the same as another's! It's important to keep this fact in mind when you answer the "what's the toughest ..." question. As such, probably your safest bet in answering this question is to preface your response with a disclaimer; "You know, I've never found any aspect of my job really tough." Then pause and continue, "On a relative scale, I think so and so is a little tougher."
As a rule of thumb, don't say that the toughest part of your job is something that would downgrade your performance if you got the job you're applying for. For example, if you were an auditor, it's acceptable to find the wait between auditing assignments tough (because it's boring). It's not acceptable to find a particular kind of auditing assignment tough if it's the kind of assignment that your prospective boss would expect you to perform.
3. What would be the toughest thing you'd have to handle in the job you're applying for?
The interviewer who asks this question assumes that you'll transfer the concerns you have about the aspects of your present job to the job you are trying to get. So one way to answer this question is tell your future boss that you don't think any one thing is likely to be overwhelmingly tough, because nothing in your present job has buffaloed you. Another way out of this one is to tell your interviewer that you'd really have to be on the job to know where the tough problems lie. It's an honest answer and your interviewer will probably appreciate your candor.
