Answer: He is afraid he would frighten or offend her.
Step-by-step explanation:
Although Odysseus wants to supplicate Naussicaa for help, he fears that clasping her knees might frighten her, him being a bulky naked mess and her a helpless youthful princess. Instead, he invokes the knee-clasp verbally ('I clasp tour knees, my queen') without touching her at all and keeping his distance.