Okay I have a question...

[Trainer of Shadows]

I am training a Cloyster.
Shellder learns Ice Shard at level 28.
Cloyster learns Spikes at level 28.
I want it to know both moves. Is this possible? How?

This is not a discussion on whether or not it should know both moves. I am teaching it those moves. So, no "Why are you teaching it IceShard?".
Got it? Good.

And to all that help me, thank you.

[ronjocox]

make Shellder learn Ice Shard. Then evolve it at LV 28. It should learn Spikes.

[Trainer of Shadows]

make Shellder learn Ice Shard. Then evolve it at LV 28. It should learn Spikes.

I was thinking this... wasn't sure if it was gonna work.
Well, thanks.

[Cool Kid 94]

It works. I've done it millions of times.

Or evolve Shellder at level 28+, and use a Heart Scale on Cloyster.