you would use the get() functionality to retreive the data. And these are not "variables" as you are calling them. they are indexing locations like in excel. you can retrieve the user input values using the last line in the code there with the get() function.
dataInput = cell(3,8);
global tableInput
figure,
pos = get(gcf,'position');
set(gcf,'position',[pos(1:2) [660 120]])
%Input table's creation
rnamesInput = {'A','B','C'};
tableInput = uitable('ColumnWidth',{70},...
'Position',[30 20 600 80], ...
'data',dataInput, ...
'ColumnEditable',true(1,8), ...
'RowName',rnamesInput);
%gen data because so i do not have to enter it in manually for the
%example
dummydata = reshape(1:3*8,3,8);
set(tableInput,'data',num2cell(dummydata))
retreivedata = get(tableInput,'data')
