。
She knows perfectly well what she should do now.
Literal
She [topic-は] now what [object-を] should-do [embedded-question-か] well knows.
~すべき is the modern descendant of classical Japanese べし ('should, ought to'), tacked onto a verb's dictionary form. Slightly literary and emphatic in tone, it's one register up from ~方がいい ('better to'). The embedded wh-question 何をすべきか pairs the interrogative 何 with か to package the whole question as a clause that the matrix verb 知っている ('know') can take. 知っている always uses ~ている for ongoing knowledge — the bare 知る wouldn't mean 'I know' but 'I come to know.'