Ticket for third country - does it have to be with confirmed seats?

Hello, I'm Lithuanian citizen, planning to travel Taipei (Taiwan) - Shanghai (Pudong) and then after 48 hours Shanghai (Pudong) - Vilnius (Lithuania) (through Moscow) and wanted to ask whether ticket Shanghai-Moscow-Vilnius has to be with confirmed seats or not? (because apparently I can not choose seats while booking ticket online and I've read that confirmed seats are required).