If I buy SC2 Wings of Liberty can I play multiplayer with a user that owns SC2 Legacy of the Void? I tried to contact the support but nothing.
Stacraft II has a feature called spawning.
Basically it means that if you party up with a player who has a higher license than you, you gain their license level. Whoever they invite to party, they are still playing their respective expansion level, and everyone else is boosted to party leader's (only while they are in a party!).
So yes, not only can you play with LotV owners, you also can play LotV with them.