first fine the repeater resides in the master page, to get the reference of repeater control use following code
Repeater rpt = (Repeater)Master.FindControl("Repeater1");
to get the object of LinkButton that resides in Repeater item use bellow code
foreach (ListViewItem li in rpt.Items)
{
LinkButton lkb=(LinkButton) li.FindControl("lnkcategory");
lkb.Enabled = false;
}
I above code will be helpful to you, if this solution comes helpful to you please give rank to me
Thanks