Hello ,
Please use this code as below ..
<asp:linkbutton runat="server" cssclass="lFilename" id="grdlinkFilename" text="<%#Eval("FILEPATH")%>" commandargument="<%#Eval("FILEPATH")%>" getpath="<%#Eval("FILEPATH")%>" oncommand="grdlinkFilename_click" xmlns:asp="#unknown"></asp:linkbutton>
You just add the attribute like GetPath as given above then write in JQuery script as below code.
alert($('#MainContent_grdlinkFilename').attr("GetPath"));