1. Stop the cursor at the position where you want to insert the trademark letter, and open the sogou input method.

2. Right-click the input method, select "Symbol Expression", and the next menu is "Symbol Daquan".

3. After the "Symbol Collection" dialog box pops up, select "Special Symbol" in the list on the left, and drop the slider to the middle position on the right to find the registered trademark letter "?" , click the mouse to insert the specified location.