If one doubts or makes a mistake in sujood as-sahu, then does he/she perform another sujood as-sahu after the salam? Please give answer for both forgetting/making a mistake in both the sujood as-sahu before salaam and the one done after the salaam.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The question is not clear enough to determine the answer to it, but if you are asking about the ruling on someone who doubts during the Prostration of Forgetfulness, whether he prostrated one or two times, or he made a mistake by prostrating three prostrations of forgetfulness, for example, then the answer is that he is not required to perform another prostration, and his prayer is valid, and there is no difference in that whether the Prostration of Forgetfulness is before Tasleem or after it.

Ar-Ruhaybani  said in Matalib Uli al-Nuha: “Cases in which the Prostration of Forgetfulness is not prescribed: if he forgetfully makes a mistake in the Prostration of Forgetfulness, he does not prostrate for this mistake. Is'haq conveyed the consensus regarding this: “in order not to lead to an endless repetition.” Likewise, if he forgets after the Prostration of Forgetfulness, he does not prostrate for that.”

An-Nawawi said in Al-Majmoo’: “If he forgets and prostrates three prostrations of forgetfulness instead of two, then he does not prostrate for this forgetfulness. Al-'Abdari conveyed the consensus of the Muslims that if he forgets in the Prostration of Forgetfulness, he does not prostrate for this forgetfulness.”

Allah knows best.