There is one Donald J Kinghorn b 1940's on WikiTree if you search under Surnames. If you open that profile, on the left hand side under the viewable details you will see a line that looks like this:
Profile manager: ___________ [send private message]
If you click on [send private message] you can email that Profile Manager directly and share your information to see if it matches the person you are looking for, you might find a long lost cousin!
If your Donald was not born in the 1940's, it would be helpful if you expanded your original question and included any of the following that you know of:
Location: Country > Province/Region/State/County - City, town of b,m, d
Dates or approximate dates of b, m, d.
Names of parents, spouses, siblings, children.
Otherwise it's difficult for anyone to help you.