The tone of a poem refers to the impact the reading has on the reader's emotions. That said, not all readers will conclude that the tone of any given poem is the same. While some may interpret a poem's tone to be one of sorrow, others may interpret a poem to speak of feelings of elation.
In regards to Michael Ondaatje's poem, "To a Sad Daughter," the tone of the poem can easily differ for different readers. Fathers who read the poem may come away from it feeling a sense of sadness and emptiness. Daughters, on the other hand, may come away from a reading of the poem feeling a sense of understanding and satisfaction.
While the daughter fails to seem sad, as the title of the poem would suggest, it seems that it is the father who feels the sadness. Given the father's words, of loss, retreat, and embarrassment, he seems to understand how his daughter may feel (at 16) with her father hovering over her. Fathers who read the poem may relate to the words of the speaker, feeling the same sense of loss and estrangement from their own daughters.
On the other hand, daughters reading the poem may relate to the desire to grow up, without the thumb of their father eternally on them.
Therefore, the tone of the poem could be any of the following: sadness, distraught, freedom, loss, enlightenment, alienation, satisfaction, and/or love.