You've got a dedicated site for this: Check shutter count online - My Shutter Count.com
Another way is to use the BEST exif reader out there: ExifTool by Phil Harvey
@just download the appropriate version, copy the "exe" to your computer's desktop, and "drag" the file containing your photo to that "exe" and "drop" it
If you'd rather not download and install another program to your computer, there is an online viewer that will do the job for you, Jeffrey's Exif viewer: http://regex.info/exif.cgi
Tons of Exif data. Search the page for "count"