Happy to share my experience and knowledge, should anyone find it helpful. U.S. bound flights have secondary, at-the-gate screening departing DOH. During the hyper nuttiness about electronics, they swabbed all electronics, then sealed them into a tamper-evident plastic bag which was nearly impossible to open. Thankfully, that era has ended.

Secondary screening at the gate for U.S. bound flights is essentially the same as regular security screening, but, perhaps, ever so slightly more comprehensive. Laptops and large electronics out of carryon bags, in separate bins. Belts, etc., off. Through the metal detector. The difference that you'll probably notice? I have found transfer screening at DOH to be a pretty relaxed affair. Yes, they do the screening properly, but the staff is relaxed and friendly. Screening at the gate is a slightly more serious affair, closer to the screening protocol at major U.S. airports. Staff is still friendly; but they are quite serious about their work. So where sometimes regular transfer screening will say OK to something, or sometimes (as has happened to me more than once) say that it's not necessary to remove my laptop from the bag, that won't happen at the gate. There's also zero chance that you might slip through the cracks at the gate screening because there is a series of colored marker lines applied to the back of your boarding pass as you go through the process indicating that you have passed a certain point or a certain examination. The coordination at the gate is very comprehensive, too. Checkin agents, security screening staff, and that final person you have to get by before entering the waiting area, are all in constant communication with each other. IME nothing gets overlooked.