Trifle recipes generally change from family to family. In my house, we don't put chocolate in the trifle, apart from a crumbled Cadbury Flake and Cadbury Chocolate Buttons or chocolate chips on top.
Here is how we do it in my family:
You need a big deep bowl, glass preferably so you can see all the layers. Ours is about 12"-14" wide but we love trifle 
Line the bowl with sponge fingers (we actually use swiss roll in ours), on the base and slightly up the sides.
Make up some jelly (you call in Jello 
) - we use tangerine flavour, others use strawberry.
Pour it over the sponge so it gets soaked. Press the sponge slightly so it soaks properly and there are no dry bits. If the sponge gets a bit crushed its no biggie.
We put tinned mandarin orange segments on top of the sponge/jelly.
This needs to be refridgerated, preferably overnight.
Make up some English custard - not sure how you do this in the US but it can either be done using custard powder, or from scratch. You should have quite a thick layer,
While it is still hot, pour it over the cold sponge/jelly.
Leave to set, again in the fridge once it has cooled down a bit.
We decorate ours with lots chopped up tangerine jelly, and mounds of cream which we decorate with garish red glacé cherries, chocolate buttons/chips, and crumbled flake. In the fridge til needed, and serve cold. We also put small meringues on the top of each mound of cream, just before serving.
You could probably look up proper recipes on the BBC Good Food website.
Here is a (not very good) picture of what ours looks like. 
Definitely agree that trifle varies enormously. If you promise to make it, he'll probably expect it to be like his mum's and may be disappointed! 
Anyway, here's how I make trifle:
Cut up chunks of home-made madeira cake (like pound cake - something fairly dense anyway, and vanilla flavoured) and place in bottom of a nice glass bowl (a punch bowl works well). Add fresh or frozen strawberries and/or raspberries (actually any berries, but NEVER anything citrus - sorry Dayti!) around the cake. Cover with strawberry jello until cake is saturated. Allow to set. Cover with a layer of cooled custard. Top custard with slices of banana, then a thick layer of whipped cream to which 2tbs icing sugar and 2tsp vanilla has been added. Decorate the top with toasted, sliced almonds, grated chocolate, whatever I have around...
Mmmm - now I want trifle for breakfast!
Many people add sherry and it then it's Sherry Trifle. The cake is sprinkled with sherry before the jello goes in. Personally I think the flavour is overwhelming, but it is very 'traditional', which is what he asked for!
Funny how the recipe changes really - I can't stand strawberry trifle! Orange is the only way for me, maybe it's from years of the same thing. I've tried it, but it's just not the same! Forgot about the sherry too - we don't put it in ours (I think it is therefore classed as a Nursery trifle, or so my Mum says), but lots of people do. I don't like it with sherry either. I agree that unless the OP gets proper instructions from her sisters boyfriend, he may be disappointed!
Use BBC Good Food Magazine's website a lot for recipes, they have loads for trifle:
http://www.bbcgoodfood.com/search.do?keywords=trifle&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=&filterItem=
I have had the Raspberry and Drambuie trifle, it is very very good!
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