Use dataTipTextRow(label,value) to add a new row to the datatip of each line object. The best way to organize this is to assign a DisplayName to the line objects that would appear in the legend (if one exists) and will be used in the DataTip. There needs to be one label for each coordinate within the line so the DisplayName value can be replicated using repmat().
Here's a demo.
clf()
hold on
h(1) = plot(rand(1,20),'-o','DisplayName','A');
h(2) = plot(rand(1,20),'-o','DisplayName','B');
h(3) = plot(rand(1,20),'-o','DisplayName','C');
h(4) = plot(rand(1,20),'-o','DisplayName','D');
h(5) = plot(rand(1,20),'-o','DisplayName','E');
for i = 1:numel(h)
% Add a new row to DataTip showing the DisplayName of the line
h(i).DataTipTemplate.DataTipRows(end+1) = dataTipTextRow('Trace',repmat({h(i).DisplayName},size(h(i).XData)));
end
