In GetData() method you are creating the data table but never returning it so I assume your compilation error is "not all paths are returning a value". It should look like this:
DataTable GetData()
{
DataTable dt = new DataTable();
using(SqlConnection Con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;AttachDbFilename=F:\AAAAAAAAAAA\FINGERPRINT\APP_DATA\QUESTIONS.MDF;Integrated Security=True;"))
using(SqlCommand Cmd = new SqlCommand("SELECT * FROM questions ", Con))
{
Con.Open();
SqlDataAdapter adpt = new SqlDataAdapter(Cmd);
adpt.Fill(dt);
}
return dt;
}
Please note I added using statements as both SqlConnectin and SqlCommand implement IDisposable.