Hi,
The tag "{LINEVAR:LOKATIE}" does not exist.
When you edit an order email, you can use the "list of available tags" button to see the list of all the tags.
There, you can read:
product_field
You can also display the value of custom fields with this kind of tags :
{LINEVAR:product.XXX}
where 'XXX' is the custom field column name.
So your tag should be "{LINEVAR:product.lokatie}" supposing that the column name of your custom product field is lokatie.
Note however that this will display the value straight from the database. For some types of fields, it won't be readable / usable. Also, you're adding a td for the value, but you also need to add it for the headers of the table.
Finally, note that if you edit your custom field via the menu Display>Custom fields, you'll find email display options there. By activating them, the custom field value will display automatically in the corresponding emails without having to customize the emails at all, with the header, and the value being processed by the field system if necessary.