I thought you meant the "collar" that is knit into the V-neck. I mean the front with V cut is done, the back is done, the shoulder seams (at least) are joined and now you want to knit the finishing touches to the V-neck? if that is what you want.... I can help.
you pick up stitches. I start in the middle back or on a shoulder seam to hide the yarn end when i weave it in. you do not want to start in the front because then you can possibly see the beginning of each round.
you want to do 2 by 2 ribbing? k2 p2? that is relatively standart.
so your number of stitches must be desivible by 4 to make a full round. pick them up nice and even and don't worry much about the count (just spread out)
in the tip of the V you either want two knit stitches or 3 (if the V is rel. narrow, just do 2 knits). [if you do 3 knits then you need multiple of 4 stitches puls 1, of course] those stitches matter in placement a little. you want them nicely evenly centered in the tip of the V.
I usually do one stitch into every cast off stitch and on a V-line one new stitch for every row. on straight lines 3 stitches for every 4 rows.
I usually take up stitches with a crochet hook and turning the string around it the SAME way with every stitch I pull trough.
put all your stitches on the circular needle and count at least once more to make sure, your total count is ok.
now mark the middle of the 2 bottom stitches down in the V. those we want to do as knit stitches. so you count: the one stitch to the right of the marker is the 1st knit stitch to count. then up the right hand side p2 k2 p2 k2 and so on. count until you reach your working yarn (middle back or shoulder seam or where ever yours ended up at...)
round 1:now you know what your first stitch to work will be. do just that ... a knit a purl.... and follow your pattern. once around.
if you counted correctly your middle stitches will be 2 knits and you will make full circle on the thing coming out with just what you need to contine aroundd.
work all the stitches as they appear (knit your knits and purl your purls)
now you need to get smaller to make the collar non-bulky.
so you take the last stitch before your "2 middle knits" and knit that one and the first knit stitch together.
now lift of the second "middle knit stitch" and knit the next stitch. pull the "second middle knit stitch" over the one you just worked.
this way you continue for as many rounds as you need to for your project.
if your V cut turned out to be too revealing (try it on, even with the needles in it) then you may have to go a few more rounds.
the 2 middle knits will just keep "eating up" the stitches to their sides as you go, may they be purls or knits so the ribbing is slanting into the middle rib nicely.
(if you do 3 middle knits for some reason you work the first knit as described, just knit the second one and work the last of the middle knits as described for the "second middle stitch")
the bind off:
I usually bind off with all knits: knit 1 stitch, knit the next, lift the beforelast over the last, knit the next, pull the beforelast over the last... and so on. but you COULD also BO in pattern. I prefer the all knit method.
if you do a k1 p1 ribbing around the neck for a finer apperarance or to match the pattern or whatever, you will still want 2 knit stitches in the bottom middle but you could also use a 3 stitch decrease with a continuos line (k2tog slip pull over??? or what was it...)
and: Don't be afraid to start over when you are not satisfied. it is normal that you are not happy with a neckline. that happens a lot.
but if it turns out to be too flared (e.g. at the shoulders) you either started with too many stitches in that spot (mark / remeber it and do less next time) or you need a decrease in this manner there too (less often)
you'll be surprised... it is a little trial and error but not as hard as it sounds.