If nobody knows the Supreme Personality of Godhead, then how He can be known? If He is not known to the demigods, if He is (not) known to the great sages, then how He can be known? Yes. He can be known. He can be known in this way. When the Supreme Lord comes before you and He reveals Himself before you, then you can know.
You cannot know by your imperfect senses. Our senses are imperfect. We have . . . several times we have described in this meeting that our senses cannot realize the Supreme Truth. Ataḥ śrī-kṛṣṇa-nāmadi na bhaved grāhyam indriyaiḥ (CC Madhya 17.136). Our senses are so imperfect that simply by expanding the sense power artificially, speculating, we cannot realize. These are described in different way in different scriptures.
So He can be known how? That is also described—sevonmukhe hi jihvādau svayam eva sphuraty adaḥ: when you become in a submissive attitude and you chant. Jihvādau. Jihvādau means the realization begins from the tongue. God realization begins from the tongue. Therefore the tongue's function is to eat and to vibrate sound. So these two processes, vibration of Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare / Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare, and eating kṛṣṇa-prasāda. You cannot allow your tongue to taste anything and everything.