The correct option is
B Knew
NOTE: The words 'today's test' explain that action is done already. Hence, we will fill in the blank with the simple past tense.
Option A - 'Was knowing' is used to define the sentence in the past continuous tense. We use the past continuous tense to explain the continuation of the action in the past. Thus option A is incorrect.
Option C - 'Did know' is grammatically incorrect here, as 'did' is used to emphasise the action. Here, the sentence wants the verb to be in the past form without an auxiliary or a helping verb. Hence, option C is incorrect.
Option D - 'Known' is the past participle form of the verb 'know'. As we need the past form, we can't use 'known' here. Hence, option D is incorrect.
Option B - 'Knew’ is the past form of 'know'. As the sentence requires the verb in simple past tense we can use ‘knew’ here. Hence option B is the correct answer.
'I knew all the answers in today's test.'