The masoretic text of Psalms 1:6 is
כִּי יוֹדֵעַ יְהוָה דֶּרֶךְ צַדִּיקִים וְדֶרֶךְ רְשָׁעִים תֹּאבֵד
Contrast with Proverbs 12:10
יוֹדֵעַ צַדִּיק נֶפֶשׁ בְּהֶמְתּוֹ, וְרַחֲמֵי רְשָׁעִים אַכְזָרִי
which the NIV translates as
The righteous care for the needs of their animals, but the kindest acts of the wicked are cruel
That is, Proverbs 12:10 uses יוֹדֵעַ ("yodea") in the sense of "to know intimately" through concern and care, something like "I feel your pain" in English, and contrasts this kindness even to animals with the wicked, who are cruel (to people) when at their best. IMHO the NIV translation does a good job of capturing the sense of the masoretic verse, but note that it requires five English words, "care for the needs of", to translate one Hebrew word, "yodea".
Pslams 1:6 uses "yodea" in the same sense. So my translation would be
YHWH maintains [cares for] the path of the righteous, but the path of the wicked will fall to ruin
That is, the path or way of is what is being watched over or not, and by implication, the righteous or wicked person.
Compare this verse with Psalms 146:9
יְהוָה שֹׁמֵר אֶת גֵּרִים יָתוֹם וְאַלְמָנָה יְעוֹדֵד וְדֶרֶךְ רְשָׁעִים יְעַוֵּת
Which the NIV renders as
The Lord watches over the foreigner
and sustains the fatherless and the widow,
but he frustrates the ways of the wicked.
where the word שומר ("shomer") to guard replaces יודע, "yodea".