The <%=txtJobAddress.Text%>
will be empty on page load. Presumably your saveChanges method prompts an ajax call to save the "JobAddress"? If this is the case then a full page postback won't occur, and therefore the <%=txtJobAddress.Text%>
isn't populated with the updated value as this would occur on the server. You'll want to populate the query string value client side
e.g. in your blur event you could add a call to a javascript function that updates your link:
onBlur="javascript:saveChanges('JobAddress'); updateLink()"
in your updateLink function you would update the link query string value