Question

[4troDev]

is there a way to have tickets open under a specify category?

[KartikeSingh]

yes, just save the id of that category and provide that category as a parent channel.
for example

guild.channels.create("name",{
    parent:guild.channels.cache.get("catgeory-id");
})

[BlobDeveloper]

yes, just save the id of that category and provide that category as a parent channel.
for example

guild.channels.create("name",{
    parent:guild.channels.cache.get("catgeory-id");
})

Or

parent: 'category id',