Lookup inputs in Flow are recreations of existing Lookup fields on an object. If you want to create a Flow Lookup input that searches for "CGT Study" records, the "Object API Name" Object needs to have an existing CGT Study Lookup field. You can create this through Object Manager if it does not already exist.
Then you set the "Object API Name" to the API name of the primary object ("Opportunity"/"Project__c"/the object to which you're trying to affiliate the specific "CGT Study" record) and "Field API Name" to "CGT_Study__c". Once complete, you will by typing the "Name" of the particular CGT Study into the Lookup field.