There are two routes to take from the Dominican Republic, either via Bermuda or closer to the Rhumb
line. You need to give us 2 pieces of information in order to get a rough estimate:
1. Boat type (and whether the Captain is going to use the engine in low winds)
2. time of year (which will determine the route and the prevailing winds)
A 50' monohull could average 140nm per day with good weather and the distance between the Dominican Republic and Cadiz, Spain is (great circle) approximately 3300nm. So a quick trip would be just over 23 days. The distance via Bermuda is several hundred miles longer, but the only route for part of the year - but it has better winds and currents, yet is usually used for trips to northern Europe. The Rhumb
line route goes through areas with variable and/or weak winds and usually one motors through, assuming sufficient
fuel reserves and willingness to use the engine(s).