What is evidence that "Zaabalawi" by Naguib Mahfouz can be interpreted as a spiritual quest, portrait of mental illness/ obsession, desperate search for companionship or support, or pursuit of self-knowledge.

In "Zaabalawi," the main character is afflicted with a serious illness that medical doctors cannot cure. Determined, he sets off on a quest to find Zaabalawi, a man who is rumored to have great healing powers. This quest can be seen through multiple perspectives, and the author leaves the reader to determine which is correct.
Spiritual Quest
The events in "Zaabalawi" can be interpreted as a spiritual quest since the main character is seeking a healer with metaphysical powers. The protagonist himself implies that his affliction is spiritual with the line, "I became afflicted with that illness for which no one possesses a remedy."
Zaabalawi is believed by many to be a holy man and, in his quest to find this healer, the protagonist himself goes on a journey that is both spiritual and physical. In a sense, Zaabalawi could represent God, while the protagonist's journey represents man's search for spiritual fulfillment and enlightenment.
Mental Illness and Obsession
Another interpretation of "Zaabalawi" is that the character suffers from mental illness. There is evidence for this in his admission that he "was overcome by despair" and his physicians have been unable to find a physical cause for his illness. Throughout the course of the story, the protagonist's focus on finding Zaabalawi turns to obsession. Although he finds some semblance of relief from his suffering after discovering Zaabalawi was with him while he dreamed, he continues to search for this mysterious figure.
Companionship and Support
"Zaabalawi" can be seen as a quest for companionship or support as the protagonist acknowledges his own loneliness and expresses a desire for friendship with Zaabalawi. He first visits one of his late father's friends in an attempt to find out more about Zaabalawi's current whereabouts and when the man mentions his father, he is overcome with sadness.

The very pain that had driven me to go there now prevailed upon me to stay.

This line implies that the protagonist is motivated by a deep loneliness and desire for companionship, and there are many examples of his encounters with the other characters he meets on his journey that you could use to illustrate this point.
Pursuit of Knowledge
A more subtle—yet equally compelling—interpretation of "Zaabalawi" is that the main character is seeking knowledge rather than a literal person. Zaabalawi embodies hidden knowledge and mystery that the main character hopes will enrich his life and heal him in both body and spirit. This theory is shown by the portion of the text in which the protagonist encounters Zaabalawi in his dream.

There was an extraordinary sense of harmony between me and my inner self, and between the two of us and the world, everything being in its rightful place, without discord or distortion.

This excerpt supports the theory that Zaabalawi represents knowledge. When the protagonist was united with him, even though it was only in a dream, he felt "a sense of harmony" with his inner self. This description coincides with many philosophical ideas about the pursuit of knowledge and the peace that comes with it.
Each of these interpretations is valid in its own right, and the story ends on an ambiguous note with the protagonist in continued pursuit of the titular "Zaabalawi." This could be seen as a metaphor for the continual process of seeking spiritual truth or knowledge. You could also take this as evidence that the main character is seeking companionship, which he finds elusive in those around him. A fourth interpretation is that the protagonist's continued obsession with Zaabalawi suggests he is still suffering from mental illness at the end of the story.
https://pls.nd.edu/assets/131608/zaabalawi/