Removing entries that have empty exData:
mask = cellfun(@isempty, newT.exData);
If I understand correctly, each row of exData contains a cell array that contains cells with variable number of numeric entries. If so then
result1 = cellfun(@(C) cellfun(@sum, C), newT.exData, 'uniform', 0)
The result would be a cell array with one entry for each row in newT, and the entries would be vectors that were the sums. If you then wanted to take the average of those sums, then
result2 = cellfun(@mean, result1)
which would give you a numeric vector, one entry per row in newT.