The Annotated Nexus - Page 54
54.1 her brothers or her mother or her sister
Stasia asks Henry is he’s ever met Mona’s siblings. Stasia understands that Mona “hates” her sister, possibly because “[s]he claims her sister is far more beautiful than she is.”
According to Ellis Island immigration papers, June (Mona) had an older brother, Herman, and two younger brothers, Sigmund and Ignatz (a.k.a Edward, with whom she would live with or nearby during her grey-haired years in Arizona). June’s big sister Gustava was also the eldest child. Later in Nexus, on p. 146, Henry will see photographs of Gustava, and will confirm that she “was even more beautiful than Mona, no gainsaying it.”
54.2 You’ve seen her on the stage
Henry nods when Stasia asks if he’s ever seen Mona on stage before. “She doesn’t strike me as an actress,” observes Stasia, noting that it doesn’t “fit” with her; it’s just another “huge fabrication” of her character.
June (Mona) did some acting in New York, late in1923. While working at Wilson’s, she had met someone affiliated with the Theatre Guild, who arranged an audition for her. She won a spot as an understudy in Saint Joan. Miller wrote about June’s theatre experience in Sexus (see. pp. 376 + 409). 
54.3 this gold-digging
Here, Statsia suggests that Henry out a stop to Mona’s gold-digging because she appears to “dig at someone just to awaken interest in herself,” and not for financial gain. Stasia finds it "disgusting." See notes at 51.1 regarding Mona’s gold-digging.
Stasia explains how Mona humiliates the men who show her any “real interest.” “Even poor Ricardo had to be tortured; she had him squirming like an eel.”
Ricardo was one of many to lavish attention on Mona. He first makes an appearance in Plexus (pp. 592, 593, 595, 597), and is described as a married Cuban philosopher of metaphysics who loves his wife and kids; “extremely poor but made lavish gifts.” He was quiet, sober, kind, gentle, and tender, yet every time he escorted Mona to the subway upon her departure, he would solemnly state, “If I can’t have you, nobody will. I will kill you.” Mona thinks Ricardo’s gentle nature makes this threat a joke, but Henry shows concern about this man’s fixation on her. Mona acknowledges in Sexus that she doesn’t show Ricardo any attention, and barely listens to him, but still insists that he and Henry are both “pure souls” who need to be protected from the world.
Later in Nexus (p. 65) Henry will meet Ricardo when he is invited to the apartment for Christmas.
54.5 take a job
Stasia continues by telling the unemployed Henry that he could save Mona if he were to “take a job” and bring home a wage so that she wouldn’t need to gold-dig. Henry does not comment on this suggestion, but soon after, on p 77, he announces that he’s going to start looking for a job soon after the Christmas holidays.
54.8 that horrible place
What would Henry’s paying job save Mona from? Going to “that horrible place every night [to] listen to all those filthy-mouthed creatures who fawn over her.” I’m not exactly sure where this specific location is meant to be, but it’s likely in Greenwich Village. It’s probably that same place where the two women put on pseudo-lesbian shows (see p.51).