get variable value on c# server side

You could store the value in a Hidden Field[^] from jquery and access it via code behind.
 
Jquery:

$('[id$="HiddenField1"]').val("Your Value");

 
Aspx:

<asp:hiddenfield id="HiddenField1" runat="server" value="1"/>

 
(or)
 
Alternatively you could use Ajax Jquery[^] to call a webservice to perform database insert.
 
(or)
 
Use Ajax Page Methods[^].
 
Hope it helps.