I wish you would confine yourself to the matter under discussion.                                                      

希望你只谈目前我们正在讨论的问题。

解答如下

to the matter under discussion 为介词短语作方面状语。使用结构为confine sb/sth to sth =sb/sth be confined to sth使某人/某事受局限于某事

(1)confine 限制(自己或自己的活动);使受局限(英文解释： If you confine yourself or your activities to something, you do only that thing and are involved with nothing else）

He did not confine himself to the one language.

他没把自己局限于这一门语言。

Yoko had largely confined her activities to the world of big business.

洋子主要是做大生意。

His genius was not confined to the decoration of buildings.

他的天赋不单体现在建筑物的装饰上。

(2)under discussion是作后置定语修饰前面的名词matter的

under discussion在讨论中

The proposals are still under discussion," she said.  

“提案仍在讨论中，”她说道。

That is completely irrelevant to the subject under discussion.  

这跟讨论的主题完全不相关.

His remarks didn't relate to the topic under discussion.  

他说的话与讨论的问题无关.

That is a plan under discussion.  

那是一个正在讨论中的计划.

Many questions are under discussion.  

许多问题正在讨论.