Hallo AnarZhan
This is not a flight, where your actual boarding is quite strictly checked at the gate. Therefore such a travel confirmation issued by the railway operator is not possible.
Even in major multinational companies, train tickets are the common/usual travel expense evidences for that particular means of transportation. (The hotel invoices from Interlaken and Milan should provide additional proof that you actually took some train that day).
However with my former employer, a company policy generally didn’t allow (cheap) non-refundable tickets (such as a Saver Day Pass) or bookings for business travel, due to the usual risk of short notice event cancellations or postponements.