How to insert in a table with only an IDENTITY column?

From the documentation:

DEFAULT VALUES
Forces the new row to contain the default values defined for each column.

So:

INSERT dbo.TABLE DEFAULT VALUES;

In addition:

1. always use the schema prefix
2. always terminate statements with semi-colons

Another way would be to use IDENTITY_INSERT. That way you can manually define which values you want to put in. Like so:

SET IDENTITY_INSERT TABLE ON ;

INSERT INTO TABLE (ID) VALUES (1), (2) ;

SET IDENTITY_INSERT TABLE OFF ;