Viewport modes are set with the icon (usually a sphere) to the left of the camera/view picker at top-right of the viewport. You can also use ctrl(Win)/cmd(Mac) plus a number key - 0 for nVidia Iray preview, 9 for texture Shaded.

To see the TopCoat parameters you will need to have the Iray Uber Base shader applied - imported geometry and Poser content will use the Daz Default Shader (3Delight) when loaded. The preset for applying the shader to selected surfaces on selected objects is in the Presets tab of the Surfaces pane under Shaders>Iray.