... ask your heart what it does know that is like my brother' s fault; if it confess a natural guiltiness such as his is, let it not sound a thought against my brother' s life!

【结构分析】

一、what it does know that is like my brother' s fault：是ask 的直接宾语。

1. it 指 your heart； 

2. does know = really knows （does 表示“强调”）

3. that is like my brother' s fault：是what 的定语从句。

【说明】what 是know 的宾语，也是that 定语从句的先行词。它作为疑问代词被前置句首时，先说主句的成分 it knows（it knows what 主动宾），然后再说定语从句。

二、a natural guiltiness such as his is：such as 表示“举例”，“像......一样的”，as 用作连词后面接从句：his is 

a natural guiltiness such as his is = 

a natural guiltiness such as his guiltiness is =

such a natural guiltiness as his guiltiness is 

【翻译】（如果良心承认）有像他的罪过这样的自然罪过（的话）