One way to do it would be to run a raid counter simulation on pokebattler, and then click "see what happens when you power up." You can then click on the individual pokemon (the Togekiss in this case), and look at how the time-to-win changes with each power up. You will also see how survivability changes, so it is useful for determining bulkpoints as well.
GamePress
Togekiss vs Palkia breakpoint for HP
Any way to find out the breakpoint calculator for hidden power? My Togekiss gets Flying HP, it's stab so the breakpoint should be different with others (Dragon HP should also be different).