請問我曾經在哪工作的英文

「曾經擔任」用 used to be 或 used to work as，「房仲公司」用 a realty company:

I used to be a secretary in a realty company.

I used to work as a secretary in a realty company.

The past continuous tense is used to express a continuous action over a specified period in the past.
eg:-I was working as a secretary in a Realty Company.
real estate is the business of selling house.Hence use Present perfect:-
eg:-I have worked in real estate (as a secretary).

To be sexy, say it this way:

I had strong and practical experience in admin assistance of realty services.