What skills are needed when carrying out an interview?

Since you say "carrying out an interview," I assume you
are asking about the skills that are needed to be an effective interviewer in a business
context.

If so, the greatest skill that is needed in
interviewing is the ability to listen effectively.  An interviewer must listen closely
to the answers given by the interview subject.  Interviewers must be able to find areas
that need to be followed up.  They must be able to have a sense of the body language of
the person being interviewed.  An interviewer who is able to listen effectively in these
ways will be able to conduct more productive interviews that are more likely to truly
determine how good a given candidate would be for the position in
question.