I don't believe that the records you need are online. However, I was able to narrow down the dates for you.
I located Doan in the 1920 census. He is listed as Don Smith in Pike County, his wife is Lindy, and her parents Johnson are living with them.
I also found the WWI Draft registration for Doan Smith. He filed in Pike Co. KY in 1918. His nearest relative was Lindy Smith.
So this puts their marriage date 1910-1918. I checked WV marriages, but did not find them. I also checked Lawrence Co.OH, where she was living with her parents in 1910. Therefore, Pike County, KY is the next likely place. They have all their marriage records indexed on their computer and may be able to check for it if you call the county clerk's office/vital records section. Ask how much it is for an UNCERTIFIED, PHOTOCOPY of the license/certificate. Probably only a few dollars. Get their address. Send them an SASE and the CASH they want. You should have it in a week or so.