"You cannot guide whomever you wish, but [it is] Allah [who] guides whomever He wishes, and He knows best those who are guided." (Qur'an 28:56)
"The Prophet and the faithful may not plead for the forgiveness of the polytheists, even if they should be [their] relatives, after it has become clear to them that they will be the inmates of hell." (Qur'an 9:113)
as salam alaikum
there is no direct reference in the above-mentioned verses about the religion of Abu Talib, neither to Abu Talib himself. The verse 28:56 is very general and says that Allah is the ultimate guide and that no one, even the Prophet, peace be upon him and his family, can guide the people if Allah doesn't wish. The verse 9:113 is also general and it is explained by its following verse (9:114) that talk about the prohibition to ask forgiveness for the polytheists, in particular it mentions the case of Ibrahim, peace be upon him, and Azar.
What made to conclude the majority of Sunni scholars that these verses refers to Abu Talib not being Muslim are some ahadith found in Bukhari and Muslim linking those verses to such opinion. There are other narrations and evidences to support the fact that Abu Talib was a Muslim: this is also an opinion held by a minority of Sunni scholars.
In conclusion, these two verses should firstly and foremost interpreted according to their apparent meaning avoiding solitary reports (akhbar ahad) which are contradictory. Then, to establish historical facts, other ways than tafsir by solitary reports should be taken into consideration in order to determine truth and valid knowledge.
With prayers for your success.