Greetings, welcome to the Forums.
First it need be said that planting distance is not an exact science. Much depends on how quickly one wants a planting to 'fill in' and the ultimate intentions for each plant regarding pruning, training, and permanence in the landscape. When two plants do bump into each other both will continue to grow. In most cases, plants will put a larger proportion of their energies into growing away from other plants and towards better-lit open space .
Ceanothus x 'Victoria (possibly synonymous with C. x 'Skylark') will grow fairly quickly to be a large shrub (6-10' H x 6-12' W). Ceanothus can be somewhat short lived, but plants that are grown in well-drained conditions with little supplemental summer water have persisted for 10-20 years or more. It will grow best in full sun.
Lemon Cypress (Hesperocyparis macrocarpa 'Goldcrest' or similar) will grow rather slowly to be a medium-sized tree. If all goes well, it should live considerably longer than the Ceanothus. It too will grow best in full sun.
Now if you wanted to plant these two plants so they only grazingly touched at maturity, you would plant perhaps, them 12 to 15 feet apart. However several questions must be asked. Will both plants reach mature size before dying or being intentionally replaced? Even if so, will the Ceanothus still be there when the Cypress approaches full size. Do you have enough room to plant them this far apart?
Do you even want them this far apart? If you do, you may want to plant other smaller or shorter-lived plants in between them.
Another idea would be to plant them only a few feet apart (say perhaps... five feet) with the understanding that the Ceanothus would be cut back and even eventually removed as the Cypress grew larger. I don't know your exact needs, wants, and parameters, but this seems like it might be the most reasonable solution. Again I encourage you to plant other smaller plants between and around these two 'anchor' plants, so as to make the bed seem full, cohesive, and generally more interesting.
