is there anything like tracing 2D image to model in Siemens NX8?
Yes there is.
Go to... View > Visualisation > Raster Image
The Raster Image dialogue box pops up with all the options.
Click on 'Specify TIFF image'
As you've already noticed only TIFF files are supported, use your favourite image editor to convert your images to TIF format.
Pick the image you want.
Now you've chosen the image, you now have to create the Raster image in the model view by clicking on 'Create Raster Image'
Then the Image will appear in the model view.
Use the options to resize, set transparency and manipulate position and angle using the Trident handles.
Apply! Then you're ready to sketch.