Before we can discuss D. H. Lawrence's Sons and Lovers in the context of an autobiographical poem, let's get a handle on what we mean by "autobiographical" and "poem."

First, when we label a work of literature "autobiographical," we're saying that the work has a strong connection to the writer's own life. If it's an autobiographical novel, as is the case with Sons and Lovers, then it might be a fictionalized version of elements from the author's life.

For example, Paul Morel is a made-up name, yet there's many elements of Paul that link him to Lawrence. Lawrence's dad was actually a gruff miner; additionally, Lawrence was extraordinarily close with his mom, and that closeness had a critical influence on his relationships with other girls. In the book, the girl is Miriam. In real life, the girl was Jessie Chambers.

There are more similarities between the novel and Lawrence's real life. As in the book, Lawrence's mom died of cancer. As in the book, Lawrence had an elder brother who died.

The above helps us see why Sons and Lovers is autobiographical. Yet what makes Sons and Lovers a poem? Clearly, it's not a literal poem. There's no stanzas, line breaks, rhyme schemes, or meter. Sons and Lovers is fiction. It's prose. Why call it a poem? Sometimes we call things a poem due to their evocative, emotional language. Are there passages that stand out as having the emotional force of poetry? We'd say yes. Here's one:

Night, in which everything was lost, went reaching out, beyond stars and sun. Stars and sun, a few bright grains, went spiraling round for terror, and holding each other in embrace, there in a darkness that outpassed them all, and left them tiny and daunted.

Why is this poetry? Again, the force with which he describes night makes us think of the power of words, which makes us think of poetry. Although, perhaps you have a different definition or an alternate example.