PostgreSQL trigger function that selects from %current% table
I suggested that you use trigger arguments, but it's actually not necessary. You can use the automatic variables TG_TABLE_SCHEMA and TG_TABLE_NAME, or use TG_RELID. These, alongside EXECUTE for dynamic SQL, let you do what you want:

BEGIN
    EXECUTE format('SELECT colname FROM %I', TG_RELID)
END;


or

BEGIN
    EXECUTE format('SELECT colname FROM %I.%I', TG_TABLE_SCHEMA, TG_TABLE_NAME)
END;


(Of course these won't work as-is, since the SELECT has no destination for the data. You have to use EXECUTE format(..) INTO ... to store the result into a DECLAREd variable), e.g.

DECLARE
    _colvar integer;
BEGIN
    EXECUTE format('SELECT colname FROM %I.%I', TG_TABLE_SCHEMA, TG_TABLE_NAME) INTO _colvar;
    RAISE NOTICE 'colname value was %',_colvar;
END;