>690
>>their real target, the Chinese securities regulator,
★knew to★ disable comments on its Weibo account on such a grim day for stocks.

ここでは、質問者がすでに分かっている通り、"know to [do something]" は
"can" とか "be able to" という意味。

こういうふうな know to の使い方は、昔は英語の中で頻繁に使われていたらしい。
しかし現代では know to do の形はあっても、know to のあとに do 以外の普通の
動詞を使う例は archaic な用法だそうだ。以下は、OED Online の解説。

know
15. trans. With infinitive as object.
a. To understand the way (to do something), to be intellectually able.
(Cf. can v.1 4.) Now arch. except with to do.

例文は13世紀からのものがあるが、古いものはすべて省略し、新しいものだけを
下に列挙する。

(1) 1870 W. C. Bryant tr. Homer Iliad I. v. 136
Who ★knew to shape★ all works of rare device.
(2) 1916 P. MacKaye Caliban by Yellow Sands 171
These hath he mastered, and ★knoweth to★ parry the white frost arrow's Pitiless barb.
(3) 1925 G. Murray tr. Aeschylus Eumenides 8
Thou ★knowest to★ hurt my soul; yea, but shalt save not him.
(4) 1956 E. Wilson Red, Black, Blond & Olive 343
The only thing they ★knew to do★ about them [sc. bugs] was to apply the torch
to the iron bedsteads.
2000 L. Gray-Rosendale Rethinking Basic Writing 2
Why was this the case? After all, I had done everything I ★knew to★ do.

OED Third Edition, November 2010 (OED Online)