This function is only available when connected to a Teradata database.
The Day of Year function is supported, returning an integer 1-366, the number of the day within a given year. When dragging a Day of Year into a variable, the following tree element is created.
Variable Creation > Input > Variables: SQL Elements pane - Calendar > Day Of Year
Columns and/or other expressions that resolve to a date can be moved over the (empty) branch of the tree.
There are no special properties for the Day of Year function.