Log in to your Salesforce platform.
On the home page, click on the gear icon and choose Setup option from the list displayed.
On the display of the configuration page, click on the tab Object manager or choose in the left menu the option Object manager.
Search the Object Manager page for the object for which you are looking for the field name. For example, you might want to see the Contact object.
Choose the option Fields & Relationships in the left menu.
In the displayed pages you can see the field name column which represents the value that you must copy in the DI platform as well as the data type which must be the same as that of the associated DI field.
You can find information on the data type here: Salesforce Field Types.