There are two places where you can find what Mission unlocks another Mission"
On the Mission page of the studio you can look underneath a Mission's description to see which Mission unlocks it.
Or you can find it under the Mission availability settings
If you need help on how to find these availability settings you can refer to this article
Can Participants in the app see what Mission unlocks another Mission?
Participants won’t be able to see which Mission unlocks another one until they complete a Mission that triggers an unlock, unless the creator has provided this information in the Mission description.