If you have your websites installed with some user statistic software then it would be easy to track them off. I would recommend for Statcounter and Google Analytics for the purpose. They both are completely free and quality. However, Statcounter does offer real time tracking while Google Analytics doesn't.
Are you asking how to see where your competition is getting it's traffic or how to see where your sites are getting traffic? If it's the latter, just install Google analytics. Other than that I don't know how to view my competitors traffic sources??
I have been using statcounter.com and it gives an exact amount of traffic comes to your sites, alongwith the ip address and the time the visitor watching your site.
He asked "other website traffic sources "??? The answer is no definite source except for Alexa, Compete and other vague ranking systems But I LOVE Alexa !!!
You cant check all sources by which your competitor is getting traffic but yet you can trace most of the major sources by simple methods. 1. Just get information about competitor website and look what are the main sources of traffic. 2. Use backlink approach. Just check the backlinks of your competitor website then you will have the clear idea from where he is getting his major traffic.
If you want to see the accurate traffic of your site use statcounter and Google Analytics b'coz it needs to install source code in your home page. For Seeing the Competitors Data use Alexa.