Question

Mallik said, “How do we know his credentials?”
(Change to indirect speech)​

Answer 1

Here is the correct answer:

Malik asked how they knew his credentials.

Explanation

It was an interrogative case.  The reporting verb 'said to' is changed into 'asked', enquired' or 'wanted to know'.When we convert an interrogative sentence starting with wh- word, we don’t add any conjunction such as ‘that’, ‘if’ etc. We just use the wh-word and turn the question into statement. The other tense and pronoun changes are applied as per the reported speech rules.