When you are logged in to ThingSpeak, click on apps, and choose MATLAB analysis. The script should appera in the list of MATLAB analysis. It is distantly possible that it was a MATLAB visualization as well, so you could look there but it sounds less likely based on what you describe of the script.
I think sharing with the original channel sounds fine if the data are related.
You could create a new channel if you expect the scraping to fail sometimes for one or the other number (perhaps if both numbers arent guaranteed to be there on every read)
The locked icon refers to the sharing status of the channel. This means noone can view the channel whom you have not specificially given access to by email address.
You can use thingSpeak Read to read from this channel if you have a read API key. See the API keys tab of your channel for the API keys for that channel.
Which channel visualization widget do you want to use?