how to add for loop in houdini16?

It should be the same as in Houdini 15.0 and Houdini 15.5: at the Geometry (SOP) level in the network editor, (i.e. inside a Geometry object), hit Tab, then type “For Loop” and hit Enter, or you can type “For Each Loop” to get one that's initially set up to loop over points or pieces. You don't have to type the whole name; just enough to make the choice unique or you can use arrow keys or your mouse to select between alternatives in the Tab menu. If you want the old For Each node, it's now called “For Each Subnetwork”. Hopefully that's what you were looking for.