In case I get stuck....?

I am taking a train from Beligum to Paris. If no one can understand me how would I ask for a train ticket from Beligum to Paris? Thank you.

Same as Amsterdam, you are very unlikely not to get someone who does not speak English.
But, just in case:
Je voudrais un billet vers Paris, si'il vous plait.


Also, remember, French speakers are not generally being snobby, stubborn, rude, total a$$clowns, etc. when they refuse to speak English to you. As a general rule, they are very interested in language and, most of all, being able to speak any language well.
Self-consciousness about the quality of their English is what causes many French speaking folks to appear as if they do not speak English at all.
Learn and use some simple French phrases and you will generally find that folks will drop their self-reserve and begin conversing with you.

No problem about 90% will speak English to you.

Een ticketje naar Parijs aub or wanneer vertrekt de Thalys? (when does the Thalys leave)

Remember: only 4 out of 10 Belgians are native French speakers!

But, you're right. Anyone working in a train station will be able to help you out in English.

Don't worry, they'll speak English!
When you are in the Brussels south station (Brussel zuid or Bruxelles midi) the Thalys leaves from platform 3 or 4...

In French it's "A ticket pour Paris", in dutch it's "Een ticket voor Parijs" so it's about the same as in English...