I worked for Thomson late 80"s to early 90's. How can I find out my retirement benefits?

How do you know there is one ? Was it company retirement or a 401K plan?
But you contact the company and ask them. If it was a "company" retirement and they have went out of business, normally the retirement goes with them.

I suggest you contact Thomson-Reuters HR department and ask whether you have any accrued pension or other retirement benefits. You can start by calling the "general Inquiries" number from their web site:

Thomson Reuters | Contact Us