Connecting 1/2 copper to 1/8 pex?
If you want to tee off the 1/2" copper line, then you can start with something like this.



Once you get down to 1/4" copper tube, you can reduce further to 1/8" tube as follows.





If you want to tee off after the sink shutoff valve, we'll need to know what size the outlet is on the valve.