Why would you want to? ADX is a number [0 … 100], SMA is a price [0 … 1.5] ADX will usually be greater on non-JPY pairs and usually less
on JPY pairs.
If you mean how to build the 10-SMA of ADX, you can do this with iMAOnArray on an array of ADX values. Or compute it with a loop:
for(int i=0; i<10; i++) sma10+=iADX(...,i);