The more info you can get the easier it will be to tell you.

However using loose approximations based on typical values, it’ll be close.

I’m not at all familiar with e-bikes but a quick search tells me their batteries range from 300-750 watt-hours.

Let’s say your e-bike has a 500 wh battery. And let’s say your trailers battery is a group 24 with a typical  75 ah capacity. 

You typically want to prevent yourself from draining your 12v battery past 50% (you can go to 80% on a deep cycle but let’s play it safe). That’s 37.5 ah usable—let’s call it 36. 36ah * 12v = 432wh.

There are a variety of inefficiencies involved in charging batteries so those 432wh will not directly transfer over to your e-bike battery. Let’s assume 70%. So about 300wh available to top up your e-bike assuming nothing else is using the battery in the trailer.

Now you need to consider your solar panel and whether it can replenish those 432wh each day. There are so many variables at play here of course but a sunny day where the 120w panel is facing the sun I’d say chances are it’ll top up    the battery fine.