Little is an adjective; a descriptive word. So is an adverb in other use but here it is adding meaning to little and 'so little' is an adjective relating to 'him'. Consider: I am better now, thank you - I am much better now, thank you - I am very much better now, thank you.What part of speech is the word "little" in the following sentence - "They knew so little about him". Is it a pronoun or an adverb. Thank you.
This adds confusion. They knew little is incomplete unless little is, say, a name.They / knew / little
so (little)
about / him
little is a noun (direct object of knew) and tells "what" they knew.
so and about / him are adjectives describing the "little"
Little could be little news, little gossip, little facts, etc. etc.
I do agree with you and Yara84. This is certainly an adverb here.I think Yara84 is correct: ‘little’ is an adverb in this context. ‘So’ is also an adverb qualifying the adverb ‘little’. ‘Little’ qualifies the verb ‘knew’. It tells how little they knew about him. It can’t be a pronoun. It’s not used as a noun here. It can’t be an adjective as it does not modify ‘him’.