I shall cite 3 verses. What I state below in terms of "plain" knowledge vs. intercourse is confirmed by Rash"i and / or other commentaries on each verse:
1 - Genesis 4:1 (excerpt):
וְהָ֣אָדָ֔ם יָדַ֖ע אֶת־חַוָּ֣ה אִשְׁתּ֑וֹ וַתַּ֙הַר֙ וַתֵּ֣לֶד אֶת־קַ֔יִן
The man 'knew' Chava his wife, and she became pregnant and gave birth to Kayin
In this verse, it mentions pregnancy and birth, so I assume that we can easily determine in this case what the word ידע means, here.
2 - Exodus 1:8:
וַיָּ֥קָם מֶֽלֶךְ־חָדָ֖שׁ עַל־מִצְרָ֑יִם אֲשֶׁ֥ר לֹֽא־יָדַ֖ע אֶת־יוֹסֵֽף׃
A new king rose over Egypt, who did not know Joseph.
Here, it means, "brain" knowledge (i.e. - not an intercourse action.) I'm guessing that since there is no mention of birth, here, we translate this as "plain" knowledge.
3 - Genesis 19:5:
וַיִּקְרְא֤וּ אֶל־לוֹט֙ וַיֹּ֣אמְרוּ ל֔וֹ אַיֵּ֧ה הָאֲנָשִׁ֛ים אֲשֶׁר־בָּ֥אוּ אֵלֶ֖יךָ הַלָּ֑יְלָה הוֹצִיאֵ֣ם אֵלֵ֔ינוּ וְנֵדְעָ֖ה אֹתָֽם׃
They called to Lot, and said to him: ‘Where are the men that came in to you this night? Bring them out to us, that we may know them.’
Rash"i on this verse (citing Midrash Rabbah) says that נֵדְעָ֖ה here means via intercourse.
While he is citing the Midrash, from viewing just the verse itself, since there is no mention of birth in this verse, how would we know what its meaning is?
For that matter, when we view a form of the word ידע how do we know what it means?