鈴木さんってもう帰ったの？って英語でなんて言うの？

If you put 退社 into a dictionary for example, you will get translations such as "leave work". However, if you are asking this question at work, everyone knows you are talking about someone leaving the workplace, therefore you do not need to mention 'work' in your question.
The main two ways to express 退社 are "go home" or "leave" (if the person you are talking to knows that you mean "leave work").

「退社」を辞書で検索すると、"leave work"などの翻訳が出てきますが、
職場でこの質問をすれば、workから帰るという意味なのが共通認識になりますので、
Did Mr Suzuki leave work already?などは言わないです。
「退社」を英語にすると、主に leave と go homeの二つの言い方が使われています。

This answer is a polite way of asking if someone has finished their work for the day and left the office or other work place.
This answer is not assuming that Suzuki-san has gone home as he/she may have gone somewhere else other than their home.

This is a respectful and non-personal way of asking if this person has left or finished work for the day.

To knock off means to stop work. To hit the road means to start a journey (in this case home). If you make tracks, it means you leave the place where you are. With all of the above example sentences you may use the past simple or present perfect form. If you use 'yet' or 'already' the present perfect form is preferred.

If you are not sure where a colleague or co-worker is you might be worried so you might ask if they have gone home you can say 'did Suzuki-san go home already?' or 'Has Suzuki-san already gone home?' if you are speaknig to a manager you might want to be more formal and not assume if someone has left and get them in trouble so you would say 'Has Suzuki-san finished for the day?'

These are all formal and common questions to ask if the person has already left. All three of these sentences can be used if you want to know if the person has left and will not be expected to return that same day. We typically use the phrases 'Has (person) gone', 'Did (person) go home', and 'Did (person) leave'. The word 'already' is optional and just refers to the person leaving sooner than expected.

Has Suzuki-san gone home for the day refers to if your coworker has left home for the day. Has left the office and gone home for the day.