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I don't think there is a way to tell with SEDO. You may be able to tell with SEDO Pro.
Can you put the domain on your server for a day and check the stats? Maybe put up a single page with adsense if losing the day of parking would be bad. My favorite for getting stats is putting Google Analytics on the page. You will see if it is direct traffic, search engine traffic, or the sites that people are following links from to get to your site.
I dug a little deeper for you and found that Sedo does indeed require you to have a Pro account in order to see where your traffic is coming from. I also found that you can go to parked.com if you have at least 10 domains you can park there and you will be able to see a traffic analysis report. It only shows the last 5 days, but it does let you see direct typeins and referers. I recommend parking there over Sedo anyway. I find my parked domains get about twice the income there, although I've only had an account there for a couple of weeks.