Three translations of this interesting saying:
Blatz: They said to him: Tell us who you are, that we may believe in you. He said to them: You test the face of the sky and of the earth, and him who is before you you have not known, and you do not know (how) to test this moment.
Layton: They said to him, “Tell us who you are, so that we might believe in you.” He said to them, “You (plur.) are testing the face of heaven and earth, and you have not recognized the one who is in your presence! And you do not recognize how to test the present time.”
Doresse: They said to him: “Tell us who thou art that we may believe in thee.” He said to them: “You examine the appearance of heaven and earth, but He who is in front of you you do not recognize, and this moment you know not how to examine!”