Learn Finnish: Laitoin nimikorttisi pöydälle. - I put your place card on the table.

The verb laitoin describes a completed action (putting the card down), so it requires a total object. Normally, this would be the genitive-looking accusative nimikortin. However, when you add a possessive suffix like -si (your), the -n ending is dropped, leaving just nimikorttisi.

Why do we use the allative case pöydälle (onto the table) instead of the adessive pöydällä (on the table)?

In Finnish, verbs of placing or putting, like laittaa, require a directional case (where to) rather than a static location case (where at). Because you are moving the card onto a surface, you must use the allative pöydälle.

How would I say "except for your place card" using the phrase lukuun ottamatta from this lesson?

The postposition lukuun ottamatta can take either the partitive or the genitive case before it. For the partitive, you would say nimikorttiasi lukuun ottamatta. For the genitive, it would be nimikorttisi lukuun ottamatta (remember that the genitive -n of nimikortin is dropped when the possessive suffix -si is added).

Is nimikortti used for both "place card" and "name tag"?

Yes. While it literally translates to "name card," nimikortti is the standard term for a place card at a table setting, as well as a name tag worn on a shirt at an event.