My friend just told me that I do not have leadership qualities. How can I know if I have them or not?

First, it is my belief that the vast majority of people can be good leaders.  So you likely can too. 

But second, if you don't think you have leadership qualities, then you probably don't.  To be a leader, people must follow you.  And your very first follower must be yourself.  You must believe in yourself so intensely that others will suspend gravity to be in your corner. 

Dave Carvajal mentioned that humility is underrated and he's right.  But not at the expense of not believing intensely in yourself.  Humility is about understanding your strengths and weaknesses.  But if you don't appreciate at least some of your strengths, it will be extremely hard for others to do so.