Should i evolve this scyther?

Evolve if you can get candy regularly because you should invest in a better one only but maybe you want a useable one right away. Don't power up.
For most people, that is an immediate transfer.

Scyther is now a raid boss and you cant get a worse one from a raid so i would say wait and save the candy. But if you are in desperate need of a Bug/Steel attacker right now, why not?

The stamina difference of a level 29 Scizor with 15 iv stamina against a 0 iv stamina scyther is 11 hp

15 stamina iv: 111 hp
0 stamina iv: 100 hp

Evolve if you are not short on metal coat. It will be useful right away without any investment.

Evolve? YES - assuming you have a plethora of Metal Coats. I've got 6 right now, I've thrown out about 10 overall because I've got 4 Scizors and 4 Steelix, I don't need any more right now.

Power Up? Not... yet. Scizor is pretty much a pure attacker right now, so the lack of HP isn't a terrible thing. If you can dodge well (not just a measure of skill, but of your cell network and phone speed), then this might be a really good Scizor. Not the best, but you're saving a hell of a lot of candies and stardust with this one.

So I'd evolve it and use it as a middling attacker. It's going to be useful in non-Solo raids (like if you get invited to a MewTwo raid, this one will likely be very useful) and even in some Solo raids it's high enough of a level to be useful as a first attacker (no dodge, just get in there against an Alakazam, get a bunch of quick damage off before it faints), but not good enough to build a team around.

I'd also ask what the current moveset is. Unless he has Night Slash, consider using him as is as a flying attacker. The double resistance to grass and fighting and triple resistance to ground are nice. And you get that for no investment whatsoever. Air slash/aerial ace are pretty good for dishing out damage.