I want to retrieve username of the logged in user from one database and add that to another database column

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;

namespace PetSittingAdoptionStore
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        SqlConnection con = new SqlConnection();
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Session["User"] == null)
            {
                Response.Redirect("~/login.aspx");
            }

            pnldogdhour.Visible = false;
            pnldogday.Visible = false;
            pnlcathour.Visible = false;
            pnlcatday.Visible = false;
            con.ConnectionString = "Data Source=sidstark\\sqlexpress;Initial Catalog=PetSitting;Integrated Security=True";
        }

        protected void rdbtndoghour_CheckedChanged(object sender, EventArgs e)
        {
            if (rdbtndoghour.Checked)
            {
                pnldogdhour.Visible = true;
            }
        }

        protected void rdbtndogday_CheckedChanged(object sender, EventArgs e)
        {
            if (rdbtndogday.Checked)
            {
                pnldogday.Visible = true;
            }
        }

        protected void rdbtncathour_CheckedChanged(object sender, EventArgs e)
        {
            if (rdbtncathour.Checked)
            {
                pnlcathour.Visible = true;
            }
        }

        protected void rdbtncatday_CheckedChanged(object sender, EventArgs e)
        {
            if (rdbtncatday.Checked)
            {
                pnlcatday.Visible = true;
            }
        }

        protected void btndogappointment_Click(object sender, EventArgs e)
        {
            con.Open();
            string strquery = "Select Username from SignUp where Username=@Username";
            SqlCommand cmd = new SqlCommand("insert into DogDayCare" + "(Username,Name,Breed,Size,FromTime,ToTime,DropOff,Comment)values(@Username,@DName,@DBreed,@DSize,@DFromTime,@DToTime,@DDropOff,@DComment)", con);
            cmd.Parameters.AddWithValue("@Username", strquery.ToString());
            cmd.Parameters.AddWithValue("@DName", txtdogname.Text);
            cmd.Parameters.AddWithValue("@DBreed", dropdogbreed.SelectedValue);
            if (rdbtndogsm.Checked)
            {
                cmd.Parameters.AddWithValue("@DSize", rdbtndogsm.Text);
            }
            else if (rdbtndogmd.Checked)
            {
                cmd.Parameters.AddWithValue("@DSize", rdbtndogmd.Text);
            }
            else if (rdbtndoglg.Checked)
            {
                cmd.Parameters.AddWithValue("@DSize", rdbtndoglg.Text);
            }
            else if (rdbtndoggt.Checked)
            {
                cmd.Parameters.AddWithValue("@DSize", rdbtndoggt.Text);
            }
            if (rdbtndoghour.Checked)
            {
                cmd.Parameters.AddWithValue("@DFromTime", dropdogfromtime.SelectedValue);
                cmd.Parameters.AddWithValue("@DToTime", dropdogtotime.SelectedValue);
                cmd.Parameters.AddWithValue("@DDropoff", clndrdogdropoff.SelectedDate == null);
            }
            else if(rdbtndogday.Checked)
            {
                cmd.Parameters.AddWithValue("@DDropOff", clndrdogdropoff.SelectedDate);
                cmd.Parameters.AddWithValue("@DFromTime", dropdogfromtime.SelectedValue == null);
                cmd.Parameters.AddWithValue("@DToTime", dropdogtotime.SelectedValue == null);
            }
            cmd.Parameters.AddWithValue("@DComment", txtdogcomment.Text);
            cmd.ExecuteNonQuery();
            cmd.Dispose();
            con.Close();
        }

        protected void btncatappointment_Click(object sender, EventArgs e)
        {
            con.Open();
            SqlCommand cmd = new SqlCommand("insert into CatDayCare" + "(Name,Breed,Size,FromTime,ToTime,DropOff,Comment)values(@CName,@CBreed,@CSize,@CFromTime,@CToTime,@CDropOff,@CComment)", con);
            cmd.Parameters.AddWithValue("@CName", txtcatname.Text);
            cmd.Parameters.AddWithValue("@CBreed", dropcatbreed.SelectedValue);
            if (rdbtndogsm.Checked)
            {
                cmd.Parameters.AddWithValue("@CSize", rdbtncatsm.Text);
            }
            else if (rdbtndogmd.Checked)
            {
                cmd.Parameters.AddWithValue("@CSize", rdbtncatmd.Text);
            }
            else if (rdbtndoglg.Checked)
            {
                cmd.Parameters.AddWithValue("@CSize", rdbtncatlg.Text);
            }
            if (rdbtncathour.Checked)
            {
                cmd.Parameters.AddWithValue("@CFromTime", dropcatfromtime.SelectedValue);
                cmd.Parameters.AddWithValue("@CToTime", dropcattotime.SelectedValue);
                cmd.Parameters.AddWithValue("@CDropOff", clndrcatdropoff.SelectedDate == null);
            }
            else if (rdbtncatday.Checked)
            {
                cmd.Parameters.AddWithValue("@CDropOff", clndrcatdropoff.SelectedDate);
                cmd.Parameters.AddWithValue("@CFromTime", dropcatfromtime.SelectedValue == null);
                cmd.Parameters.AddWithValue("@CToTime", dropcattotime.SelectedValue == null);
            }
            cmd.Parameters.AddWithValue("@CComment", txtcatcomment.Text);
            cmd.ExecuteNonQuery();
            cmd.Dispose();
            con.Close();
        }
    }
}