I have made an iOS app which shows ads from multiple ad networks.
iTunes Connect asks me to give a rating of this app based on its content, and I am not sure wether I should consider the ads as a content, since they come from a third-party service and I have limited (or no) control over them.
In case the ads are considered a content, how am I supposed to know which kind of ads show up and how frequently, since the ad networks I implemented do not offer this kind of informations?
I looked both on google and stackoverflow but could not find an answer.
You're certainly going to be responsible for whatever content your own application displays. If your vendors can't provide any information on their content, you need different vendors. There should be content guideline documentation available from any reputable vendor. See Apple's, Project Wonderful's, and AdMob's for examples. Ad vendors certainly can and should be rating or restricting their content so that you can control what you serve. If they're not, you shouldn't work with them. It's just going to be trouble on you.