We can't answer that: we have no idea how you want to display the information.
The easiest way is to add a table of some form to your page (A GridView should do) and bind it to the datasource.
But without knowing what you are trying to achieve, we can't really help.
BTW:
Do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.
SqlCommand cmd = new SqlCommand("select username from registration t1 FULL OUTER JOIN result t2 on t1.username=t2.total where username=@UN", con);
cmd.Parameters.AddWithValue("@UN", TextBox1.Text);