You usually see your download numbers in itunesconnect and therefore you can just invite your clients to look into the data there. There are also a number of web services that use the data from itunesconnect to show more details, for instance app statistics.
If you want more data and even logging, many users integrate additional logging features in their apps like google analytics for instance.
If this is not what you are looking for, please give me some more information on what you are trying to accomplish!