Titration Curve Problem for amino acid

(20 points) Draw the titration curve for the titration of 25 mL of a 0.18 M solution of lysine (pka1 =
2.18, pKa2 = 8.95) with 0.15 M sodium hydroxide. Clearly label the axes of your graph in mL of
sodium hydroxide added. Be sure to include pH values and volumes for the following: Start of the
titration (no sodium hydroxide added), the pH at the volume that is half of the volume of the
endpoints, pH and volume at the end points of the titration, the pH of the solution when 1 more mL of
the sodium hydroxide (past the final end point) has been added. Show all of your calculations.

I know how to do everything but I cant seem to find the endpoint!! I have no idea which Kb value to use. Any help would be appreciated!