You can do it by using the below 3 solutions
Solution 1 :
<asp:TextBox Runat="server" ID="TheNotes"
Text='<%# Bind("notes") + Bind("dates") %>' />
Solution 2 :
You can do one more things, u can select two column as a single column in sql select query.
SELECT (ColumnA + ColumnB) AS ColumnZ
FROM Table;
and then bind it with single control
Solution 3:
bind multiple data to itemtemplate in gridview using Row data bound
And