FAQ Night Train: Can I smoke on a night train?
Smoking on night trains: what is (not) allowed and where you can smoke.
No, and this also applies to electronic cigarettes on almost all trains. If you smoke anyway, you will be fined.
You can use the layovers to get off the train and smoke. However, depending on the country, smoking is only permitted in certain areas of railway stations or is prohibited altogether. Also, note that the intermediate stops are not always as long as indicated in the timetable. Stay close to the train door and pay attention to the train crew. More information about layovers here.