This bookmark is unusual - it's not rectangular! The wave pattern is created by having increases on one side and decreases on the other - then flipping sides. Because of the wave, the bookmark has an illusion of width and complexity, but is a relatively simple lace pattern that knits up quickly.
The pattern is Japanese Feather from Barbara Walker's 2nd Treasury.
1 (partial) skein Patons Grace (1.75oz/50gm to 136yds/125m) 100% mercerized cotton (shown in Rose), CYCA size 3
US 3 (3.25mm) knitting needles
Cast on 12 sts.
Row 1 (and all wrong side rows): K1; P10; K1
Rows 2 and 4: P1; K10; P1
Row 6: P1; K1; (YO K1) three times; SSK three times; P1
Row 8: P1; K1; (K1 YO) three times; SSK three times; P1
Row 10: as Row 6
Row 12: as Row 8
Row 14: as Row 6
Rows 16 and 18: P1; K10; P1
Row 20: P1; K2Tog three times; (K1 YO) three times; K1; P1
Row 22: P1; K2Tog three times; (YO K1) three times; K1; P1
Row 24: as Row 20
Row 26: as Row 22
Row 28: as Row 20
Repeat these 28 rows again.
Work 5 rows of stockinette stitch (purl on wrong side; knit on right side).
Weave in ends.
Block; I used some spray starch to stiffen the bookmark slightly and pressed using a steam iron.