The best description of the process that occurs when nuclear DNA codes for a protein in the cytoplasm is:
mRNA is transcribed from DNA and leaves the nucleus to be translated by tRNA in the cytoplasm.
This process involves transcription, where a messenger RNA (mRNA) copy of the DNA is made in the nucleus, and then this mRNA exits the nucleus to the cytoplasm, where it is translated into a protein by ribosomes with the help of transfer RNA (tRNA).