Condition: jumps if PF = 0, that is when the lowest 8 bits of the last result hold an odd number of 1 bits. JPO ("parity odd") names the same instruction. Logic instructions are the usual way to set PF from a value, since MOV changes no flags.

Prints Y. "A" (41h, two 1 bits) prints N.
MOV     AL, "C"  ; 43h = 0100 0011: three 1 bits
TEST    AL, AL
MOV     DL, "Y"  ; MOV leaves the flags alone
JNP     SHOW1    ; taken: DL stays "Y"
MOV     DL, "N"
SHOW1:
MOV     AH, 02h  ; DOS: print the character in DL
INT     21h

The textbook use is making a 7-bit character even-parity for a serial line: if the count of 1 bits is odd, set bit 7 so the total becomes even.

AND     AL, 7Fh  ; seven data bits; sets PF
JPE     DONE1    ; already even
OR      AL, 80h  ; add the parity bit
DONE1:

Range

On the 8086 JNP exists only in the SHORT form: two bytes, opcode 7Bh and a signed 8-bit displacement counted from the end of the instruction. The target must lie within −128..+127 bytes of that point. To go farther, invert the test and hop over an unconditional JMP, which can reach the whole segment. MASM 6 makes this rewrite itself when it finds the target out of range (its default OPTION LJMP), so the listing may show two instructions where you wrote one.

JP      SKIP1    ; the opposite test, a short hop
JMP     FARAWAY  ; any distance in the segment
SKIP1:

Later CPUs

The 80386 added a near form of every conditional jump, 0Fh 8Bh followed by a 16-bit displacement (32-bit in 32-bit code), so from the 386 on JNP can reach anywhere in the segment. Code for the 8086 must stay with the short form.