It says veyadata es Hashem elokecha And ladas ki Hashem hu Elokim devarim 4:35
What does it mean to know Hashem (God)? How can our finite and limited minds grasp him and understand him?
Not Hashem's Torah, Hashem Himself.
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study the divine wisdom in nature as the chovos halevavos shaar yichud ch.10 says
Therefore, you should exert your mind until you know the Creator through the evidences of His works and not strive to know Him in His glorious essence. For He is exceedingly close to you from the side of His deeds but infinitely remote in any representation of His essence or comparison with it. As already stated, we will never be able to find Him in this way. When you arrive at the stage where you abandon (trying to find Him) through your thoughts and senses because He cannot be grasped in this way, and you instead find Him in the evidence of His deeds, as though He were inseparable from you - this is the pinnacle of knowledge of Him which the prophet (Moses) exhorts us on in saying "Know therefore this day, and consider it in your heart, that the L-ord He is G-d in heaven above, and upon the earth beneath: there is none else" (Deut. 4:39).
in Gate 2 regarding knowing the unity of God, one can notice this in the universe as he says
For [divine] wisdom, though varied in its manifestations in created things, is fundamentally and essentially one - just as the sun is one body, while the appearance of its rays when passing through glasses that are white, dark, red or green, varies and assumes respectively the color of each medium, and just as water with which a park is sprinkled assumes the color of the blooms on which it fall
i.e. the nature of wisdom is the same everywhere. be it a blade of grass or an ant or an elephant or even an atom, it is all the same character of wisdom. namely divine wisdom, one can spend years and years studying it and never fully understand how it works. though modern scientists assert it is all an accident and no intelligence was involved, they are finding out the hard way just how ridiculously complex each and every thing truly is. even the "simplest" bacteria turns out to be an intense world of bewildering complexity. you may like this for more.
Jeremiah (9:22-3) states:
ירמיהו פרק ט (כב) כֹּ֣ה׀ אָמַ֣ר יְקֹוָ֗ק אַל־יִתְהַלֵּ֤ל חָכָם֙ בְּחָכְמָת֔וֹ וְאַל־יִתְהַלֵּ֥ל הַגִּבּ֖וֹר בִּגְבֽוּרָת֑וֹ אַל־יִתְהַלֵּ֥ל עָשִׁ֖יר בְּעָשְׁרֽוֹ: (כג) כִּ֣י אִם־בְּזֹ֞את יִתְהַלֵּ֣ל הַמִּתְהַלֵּ֗ל הַשְׂכֵּל֘ וְיָדֹ֣עַ אוֹתִי֒ כִּ֚י אֲנִ֣י יְקֹוָ֔ק עֹ֥שֶׂה חֶ֛סֶד מִשְׁפָּ֥ט וּצְדָקָ֖ה בָּאָ֑רֶץ כִּֽי־בְאֵ֥לֶּה חָפַ֖צְתִּי נְאֻם־יְקֹוָֽק
22 Thus saith the LORD: Let not the wise man glory in his wisdom, neither let the mighty man glory in his might, let not the rich man glory in his riches;
23 But let him that glorieth glory in this, that he understandeth, and knoweth Me, that I am the LORD who exercise mercy, justice, and righteousness, in the earth; for in these things I delight, saith the LORD
(Mechon Mamre translation).
In that case, at least, knowing God evidently refers to imitating him, by practicing charity and the like.
Although this seems like the natural reading of these verse, that does not need further support, Radak on the verse understands it identically:
וידיעת האל היא ללכת בדרכיו לעשות חסד משפט וצדקה כי כן עושה אותם הוא
Knowledge of God is going in his ways to do kindness, justice, and charity, for such does He do.