Unless they specify it be a fictional RESTAURANT report, I would send them a report that was highly detailed in its observations from something you are comfortable with.
Generally a restaurant report is looking at exterior observations--condition of building and lot, signage and lighting, cleanliness of it all including the front doors.
Inside you are commenting on the promptness and courtesy of the host/hostess, the accuracy of their stated wait time, whether they chatted with you as they escorted you to a table, whether their pace to the table was appropriate for you. In fine dining they are going to want to know about chair and napkin service. In all of them, the host/hostess needs to present the menus/wine lists and often mention the evening's specials.
Then the timings begin--from departure of the host/hostess, how long to be greeted by your server and what was the greeting (and did they introduce themselves)? Did they suggest beverages, appetizers? If so, what? Did they recommend specials and other entrees from the menu? Did they describe preparation in appealing ways? Did they answer your questions/take special requests from you? From order, how long for beverages, appetizers, entrees? Did they offer you dessert and coffee? If you ordered dessert, how long for delivery? Throughout did items get delivered to the correct guest, usually ladies first, without 'auctioning' them at the table? Did beverage glasses get refilled appropriately? (some places it is when half empty, some 3/4 empty, some don't specify).
Describe each item served in plating, smells, temperature, quality of ingredients, flavor and whether prepared as you requested.
Was the bill appropriately presented (usually in a check presenter) and accurate? Once you set out payment, how long to be picked up and how quickly was your credit card returned? What did your server say?
Did you see the manager and what was he/she doing? (Working with staff, visiting guests, escorting guests to tables, bussing tables, delivering items to tables?)
Generally you need a description of your host/hostess, the manager and your server. You may need names as well for some or all of these, but definitely for your server. Some shops you need a description of the bus person(s) and how quickly and efficiently they cleared a table and got it reset.
You usually need an evaluation of the cleanliness and freshness of utensils, china and glassware, your table, the condiments and decor on it, etc. The floor needs to be clean and the decorations and lights need to be clean and working. The background music, temperature and lighting get evaluated, as do restrooms.
When you leave, did the host/hostess say anything to you, or other employees say anything?
And of course you need the time in and the time out. Often you also need to evaluate how full the restaurant was on arrival and departure.
Restaurant narratives tend to be quite long, especially for the high end ones where there often are relatively few Yes/No questions but an expectation of several thousand words of narrative. Often the higher end casual and high end also require a bar visit and/or an evaluation of wine service and recommendations at the table.
Realize that a high end restaurant can readily have a reimbursement of between $200 and $250 for a dinner for two. Some of the companies are excruciatingly slow to pay and you have to hound them. I am currently hounding Freeman for around $200 for a job done more than two months ago. I have pretty much stopped doing their upscale hotels/resorts/spas just because it takes so darn long for them to pay. With the current restaurant job, I have about decided to stop doing those as well. (Last year I had more than $2300 open on my books and credit card for a single resort job for them for more than 6 weeks when their specific information was that the resort bill would be backed out in a week to 10 days, with payment in 30 days for fees and other reimbursements.)