As the trial uses online licensing, you can install Tekla Structural Designer and activate your trial license on any machine with an appropriate version of Tekla Structural Designer installed and an internet connection. Then simply log in with your Trimble ID when you launch the program to utilize the trial license.
However, the trial license is locked to a specific Trimble ID, as well as a specific computer, once it is activated. The license is locked to the Trimble ID upon activation, and is locked to the first computer used to access the software with that license. It cannot be transferred from then on.
Anyone can get a trial license, so if you have a colleague or friend who wants to trial Tekla Structural Designer, they can sign up for themselves. You should also use the trial license for the first time on the machine you intend to use for the duration of the trial.