For radio emisions, do we need to certify the hole board (FCC, CE) even if the radio already has this certification?
Yes, since if you add electronics next to a radio module you affect EMC. And notably, it is impossible to reason as "the supply to my radio doesn't affect EMC or radio characteristics" - it always does. Regarding "certification" only FCC (and Canada) hand out actual certification (and bill you some $2000+ extra just for the certification fee). In EU you don't have that, but just test house reports against various EN/ETSI standards.
What you don't have to re-do is technology-specific certification (like for example Bluetooth conformance or similar), given that you also use the antennas recommended by the manufacturer.
Our product is a module that will be plugged in other specific devices. For different devices we have different wire harness. The board will be the same but we will have different wires. Do we need to certify the board with the wires (multiple different certifications) or can we just certify the board and use different wirings?
I would reason as: pick the worst-case scenario and test that one, then document that this should also cover the other cases. However, in case you need to perform conducted emission/susceptibility tests, that might not be enough, as the test house will have to do at least one test per wire type and/or signal type.
I guess the answer for this question will be "Yes" but... If we have the exact same product (radio module, RTC, ROM,...) but we have different PCBs shapes (and different connectors), we need to do certification for each of the boards?
Here as well: keep a document about EMC compliance in your product's technical file (to be made available to test houses and authorities) where you reason about product changes carried out after EMC testing and your rationale regarding why you still believe the product is conforming after the change.
For example a PCB re-design that change RF traces, ground planes, antenna grounds etc will definitely affect EMC and radio, but changing the shape of some non-critical parts probably won't. The thing with EMC in general and radio in particular is that pretty much everything in the product turns into an EMC-related component, including housing, metal parts present near antennas, the antennas themselves, cables acting as antennas etc etc.
For Europe, the CE includes the radio and de EMC. But for USA and Canada the FCC/IC is mandatory for radio emisions, but for EMC do we need some mandatory certification to sell our produc? I heard the UL is not mandatory but is very very recomended and we will like to do it. Information about UL certification will be very apreciated.
Radio approval should implicitly cover EMC. For example if you CE mark according to the RED directive, then the EMC directive does not apply (since RED covers the same standards but have tougher requirements). With FCC/IC it should be similar although it might depend on which radio band you are using, if it is license-free (part 15) or licensed (some other part, maybe 90). Either way the test house will know these things (much better than I) and suggest the applicable tests.
Notably, doing all tests for CE/FCC/IC all at once at the same test house has some economic benefits, since hiring the EMC chamber is the biggest cost. And the engineer doing the tests won't have to re-learn what's specific to your product for each test.
UL isn't required unless you have specific product requirements. For example it is highly recommend for product like 230 VAC supply converters. The RED directive does mandatory include the parts in the low voltage directive (LVD) that are related to electrical safety requirements. But this is a joke because you can self-certify CE marking/LVD - so UL has become an "I actually tested my product for electrical safety" stamp in some branches, like the mentioned AC/DC voltage supplies.
For some generic radio product, you likely don't need UL. It's main purpose is not technical, but to act as a trade/export obstacle.
