Hi Josette!
Without having exact travel dates, it is a little difficult to give you a concrete answer, but I'll do my best!
At the Magic Kingdom and at Epcot, there are almost always nightly shows which feature fireworks. Depending on the time of year you visit, there may be holiday parties at the Magic Kingdom which would require a separate admission in order to see the fireworks from within the park.
The only caveat I will give you is that in cases of extreme weather show are subject to cancellation.
At Hollywood Studios, Fantasmic is performed multiple times per week, but, in general, it is not scheduled for every night.
The online
Park Calendars for each park will list the nightly shows and are your best bet for planning. Of course, it is a good idea to double the calendar after you arrive at Walt Disney World just in case there are last minute changes.
Hope this helps!