Expressing 'about' in Chinese
[About + adjective phrase]= [有关 + adjective phrase + 的] or [关于 + adjective phrase + 的]

'My teacher taught us (knowledge) about Chinese'
我老师教我们有关中文的 (知识)
'Chinese'(中文) is a part of the adjective phrase '中文的'
The object '知识'(knowledge) can be omitted in English, but cannot be omitted in Chinese.
有关 can also be omitted: 我老师教我们中文的 (知识)

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‘My friend was telling me (things) about Chinese'
我朋友告诉我有关中国人的(事情)
'Chinese'(中国人) is a part of the adjective phrase '中国人的'
The object '事情'(things) can be omitted in English, but cannot be omitted in Chinese.
有关 can be omitted: 我朋友告诉我中国人的(事情)

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'You're not intelligent enough to talk about complex Chinese grammar'
你还没聪明到能够谈论有关复杂的中文语法的(程度)
'复杂的中文语法' (complex Chinese grammar) is a part of the adjective phrase '复杂的中文语法的'
The object '程度'(level) can be omitted in English, but cannot be omitted in Chinese.
有关 can be omitted :你还没聪明到能够谈论复杂的中文语法的(程度)

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'The novel is (a novel) about dragons'
'这小说是关于龙的(小说)'
'龙'(dragons) is a part of the adjective phrase '龙的'
Since the object 'novel'(小说) is the same as the subject, it can be omitted in both English and Chinese.
有关 can not be  omitted here -- because 龙 is a noun that can be either part of the adjective phrase or the subject. '这小说是龙的(小说)' could mean 'it is a novel about dragons' or 'dragons own this novel'