Since there are two different Ka values, the first midpoint occurs at pH=pKa1 and the second one occurs at pH=pKa2.
sˈɪns ðɛɹˌɑːɹ tˈuː dˈɪfɹənt kˈɑː vˈæljuːz, ðə fˈɜːst mˈɪdpɔɪnt əkˈɜːz æt pˈiː ˈeɪtʃ ˈiːkwəlz pˈiː kˈɑː wˈʌn ænd ðə sˈɛkənd wˈʌn əkˈɜːz æt pˈiː ˈeɪtʃ ˈiːkwəlz pˈiː kˈɑː tˈuː.