What do you do when a spell or something says that the target needs to do a saving throw without a number for the throw? [duplicate]

For command, it states, "The target must succeed on a Wisdom saving throw or follow the command on its next turn" without any context to how high the target needs to roll for it to succeed. What does the target need to roll to succeed that saving throw? Is the number specific for command or is it the same for all spells like this? I’d like to get all the info I can for this.