How and where to add a dc blocking capacitor for a gps loop antenna?
Is the antenna on a connector? If so then you can get off the shelf DC blocks e.g. http://194.75.38.69/products/dc_blocks.shtml which will do the job without having to mess with strapping capacitors onto the board. The minicircuits web site is fairly poor but they are a good starting point for any basic RF building blocks, obviously other brands/vendors exist.

You could easily create your own connection PCB with a capacitor on (from memory for GPS frequencies a 15pf 0603 works well) however the time and hassle of getting the impedance matching and shielding as good as the off the shelf products is normally not worth any potential cost savings.

You can also get Bias-Ts which block DC on the RF path but also provide a DC port that allows you to supply power to one side of the connection. They cost a little more but are a more useful thing to have in your stock of RF bits and pieces.