Member's name in triggered email?

Okay, then look in the Wix Users API and it will show you how to find the name of the user.
https://www.wix.com/corvid/reference/wix-users.User.html

Just change the field key lastName to name from the collection etc.
https://support.wix.com/en/article/corvid-wix-members-privatemembersdata-collection-fields#name-name

How can I get the current user’s name?
Use the currentUser property to get the current user’s id .
Then query the Members/PrivateMembersData collection for the item with that _id.

wixData.query("Members/PrivateMembersData") \
  .eq("_id", wixUsers.currentUser.id) \
  .find() \
  .then( (results) => { \
    lastName = results.items[0].lastName; \
  } );