When pronouncing the plural form, the letter "k" is pronounced, followed by the long "ai" sound and the "vz" sound for the letter "v" in the plural form. Thus, it is pronounced as "nai-vz."
The "k" sound is produced by touching the back of the tongue to the soft part of the roof of the mouth, while the "ai" sound is a long vowel sound similar to the word "eye." The "vz" sound is produced by vibrating the vocal cords while making the "v" sound, followed by the "z" sound.
To summarize, the plural form of "刀子" (knife) in English is pronounced as "knives" (nai-vz).