//if you have exactly one <Ticket> with exactly one <Reason>
string strReason = xmlDoc.Descendants("Ticket").Single()
.Descendants("Reason").Single().Value;
//if you have one or multiple <Ticket> elements,
//each with exactly one <Reason> element
string[] astrReasons = xmlDoc.Descendants("Ticket")
.Select(ticket => ticket.Descendants("Reason").Single().Value).ToArray();
//if you have one or multiple <Ticket> elements,
//each with one or multiple <Reason> elements
string[] astrReasons2 = xmlDoc.Descendants("Ticket")
.SelectMany(ticket => ticket.Descendants("Reason")
.Select(reason => reason.Value)).ToArray();