What profession could this woman have?

She was a very attractive young woman 28-35

She works with a laptop and travels between Berlin and Frankfurt.

What could the profession be?

That can be anything from callgirl to insurance marketer.

Do you really believe that one can recognize a profession with such information?

That can be many. Because Frankfurt would I say times possibly in the banking to do.
Vlt. Also insurance company. It represents, as well as possible, an international consortium in the investment and marketing industry.

Everything, account manager for Germany, journalist, engineer, all IT professions…, managers, HR managers, representatives, designers…

If you had not written the age and "very" at it, I could have been too ;-) In the train I also use the travel time to work.
You can always do something productive, which benefits the marketing, the websites… Even without social media is always something to do on the to-do list!

She leads seminars for secretaries such as "Assistant 4.0" etc.

Then there are several assistants in Frankfurt from Frankfurt, in Berlin several from Berlin, in Hamburg which from Hamburg etc.

That could be virtually anyone. Maybe she is also a carpenter and has made her tax return during her free time.

Politician? Because of Berlin?
Maybe she just buys a car in Berlin or flies from there on vacation.

You know your way around.

And how does she usually find her partner?

Cliche.

In public transport certainly not.

On a dating platform, matching the laptop - where we cheerfully down the clichés.
Why do not you invite them to the on-board bistro for coffee?

If you do not know how to address this woman, you just ask if she has such bad internet at DB…
And you'll get an answer. Start of conversation reached.

Why not? It's not so outlandish.