This is a very old thread, so typically they don't get as much engagement. Generally it's better to open a new thread than ask a new question in an old thread, especially when the old thread already has a marked answer.
That said, I'm still happy to help.
//Get id of parent GridRow for the link that was clicked
rowIndex = $(sender).closest(
//Parse the row index from the ID (probably a better way to do this I'm still missing...)
rowIndex = rowIndex.substr(rowIndex.lastIndexOf(
) + 1);
firstMasterTableViewRow = $find(
"<%= RadGrid1.MasterTableView.ClientID %>"
"ExpandThisMasterTableViewItem(this); return false;"
Notice the "this" being passed to my JS function. That's the sender element. You also see that I've switched from using a LinkButton to just a standard HTML link. If you're only using these links to fire client-side actions, there's no real need for the server control. Still, you could modify your OnClientClick definition just the same if you want to continue using LinkButtons.
Now, when one of these link buttons is clicked, the detail table associated with the row is expanded.
Hope this helps.
I should note that I'm using jQuery to get the ID of the parent grid row element. You can do this without jQuery, but the jQuery approach is a bit more robust.