Hi,
There is no placeholder for company name. BTW, I am wondering why you are looking for a placeholder for company name? Does your company name change between different offers?
But if you do want to set a placeholder for company name, I tested a little bit in my environment and hope this helps.
For example, we can do the following:
Go to library, create a new section and add an offer data. Name this offer data “CompanyName”.

Go to offer data rules and upload offer data rules. Offer data rule specifies the values you can choose from when creating an offer.

The file should be in cvs format. For example, below is the data set I created for testing purpose:

Then we can test it. Go to template and insert the placeholder into to a template.

After that, using that template and create an offer. Select a value for CompanyName.

Then we can see the value is auto-populated in the offer;

More details can be seen at:
https://docs.microsoft.com/en-us/dynamics365/unified-operations/talent/offer-setup#offer-data
Regards,