Some of the best things that a city has offer can be found by mistake.原文翻译：城市里有些绝佳经典可能误打误撞发现的that a city --在这里怎么理解?has offer --在这里怎么理解请说说主谓宾?

这是一个由that引导的宾语从句
句子为主系表结构分析为：
some of the best things（主语部分）
that a city has offer（修饰主语）
can be found （谓语部分）
by mistake（表语部分）
其中先行词是things 由that引导的宾语修饰
a city has offer在句中是一个现在完成时翻译为“一个城市所给予的”
不过这个形式是错误的正确的形式应该是a city has offered

Some of the best things that a city has offer can be found by mistake.
主语:some of the best things
谓语:can be found
没有宾语。
that a city has offer 做主语的后置定语。意思是，城市所能呈现的最美好的景物。。。。

that 在这里引导后面的从句,做先行词使用,修饰best things