In the poem "Breaking Out" by Marge Piercy please explain the lines "Nasty stork king of the hobnobbing doors was a wooden yardstick dusty...there were things I should learn to break."

This poem is a personal exploration in which  the poet reflects upon a repressive abusive childhood when she was disciplined with corporal punishment. Corporal punishment is a less common method used in child rearing now, and many people of previous generations, including writers and artists, describe related experiences in their work based upon how their own formative years were affected by it. Pierce was obviously deeply affected by these experiences and the poem is generally reflective of the theme of female empowerment.
This stanza introduces the object used by her parents to discipline her: a yardstick (made of lightweight wood and used for measuring):

Nasty stork of the hobnobbingdoors was a wooden yardstick dustywith chalk marks from hem’s rise and fall.

The "nasty stork" describes how Piercy's young mind saw the stick standing in the corner. "Hobnobbing" is a word that means socializing or fraternizing, as with other social circles, perhaps doors that separated servants from the family. The yardstick is "dusty with chalk marks" that show its use for hemming garments as someone stood on a chair. The idea that an object used for a mundane purpose such as hemming a skirt, and also for beating, underscores the daily stress and fear Piercy lived with as a child, constantly reminded of the potential for corporal punishment by this object she saw frequently. She tells us in the next stanza "that stick was the tool of punishment."
In the next stanza she describes her parents different levels of intensity using the stick, and how she would inspect her bruises afterwards, seeing them as "red and blue mountain ranges" and visualizing the veins as a map that would guide her eventual escape from this abusive upbringing. She then describes taking the ruler (yardstick) at age eleven and smashing it to "kindling" (an image that conjures burning, a powerful metaphor for transformation).
She becomes "an adolescent not a child" when she owns her power and destroys this implement of pain. Her comparison to herself as Sisyphus, the Greek character from mythology who is condemned to roll a boulder uphill again and again, is meant to emphasize her escape from torture, and her empowering act of breaking through her pain and oppression.