Your interviewer is looking to hear that you are cognizant of many aspects of the job where you would need to work harder to come up to speed to be fully competent. Given that the eLearning Development field is relatively new and growing, your interviewer isn't expecting to hire someone who can come in and have every aspect of the job mastered. Before your interviewer, be sure to read the job description thoroughly and be honest with yourself about the most significant potential hurdles. As you answer, do your best to turn this initial weakness into a growth opportunity. Show that you are willing to put in the time and effort to become fully capable in this role.