This is also a question that you have to consider beforehand and have a prepared answer. Besides the fact that the interviewers will want to see if your strengths match the profile they are looking for, they would also like to understand whether you are mature and confident.
Hmm, the strong ones you will name easily. What about the weak?
Do not make the mistake of saying that you can not remember. This speaks of a lack of adequate self-esteem, inability to think fast and to communicate.
The internet is full of tips that tell you to choose something that is seemingly negative, but it is actually positive - like, for example, that you spend more time than needed to do important tasks in order to make sure that management gets the most relevant information.
That sounds artificial, doesn’t it!
Remember, this is not a confession or therapy. The real question is to what extent you know yourself and can objectively find and improve the not so strong areas of your skills and character.
So, pick something that is not key to the position you are applying for and add what you have done to improve this flaw. If you are applying for the position of an accountant, for example, most probably it wouldn’t be of key importance to you to be a highly competent speaker who makes public presentations.