dominance- which one is dominant?

We've had Sky (collie) since a pup and we've had Bo (rescue Jack Russell) for six months. Bo has alot of problems with dog aggression and hates strange dogs on sight. When i took him to a trainer she was asking me which dog was the dominant one, well i don't really know and after talking to her she said that she couldn't tell either. There aren't any aggression issues between them but it would be interesting to find out whether Sky the softie or Bo the nervous aggressive is top dog in our house? Any thing i should be looking out for? If Sky is eating out of his bowl and Bo goes over then Sky will just move over for him but Bo will also do the same to Sky! If one is asleep on the other side of the room then they are both as likely to go over for a cuddle up, Sky is just as likely to chase Bo as Bo is to chase him so i really can't decide! Are they likely to be on the same Footing?

Does one dog lie on their back when playing more so than the other? Cower so their head height is lower than the other? They both may show submissive actions to each other, but you need to see who does is it more to find out.

Do they 'hump' each other?

This is also a sign of dominance.

Sorry forgot to ask how old are they? Do have a dog and a bitch? Or 2 dogs?

Two dogs roughly same age Bo has been neutered Sky hasn't. Haven't seen any 'humping' but we've always said that because Sky is a 'Proper' Welsh collie that he may be the only gay in the village coz i don't think he knows he has 'bits' yet let alone know what to do with them!!!! He wasn't even interesed in Mother-in-laws bitch when she was in season but her other dog (neutered) and Bo (neutered) were going scatty around her! Perhaps he's just so laid back that he doesn't care.

It's thought now that dogs often have a very fluid pack order so that some may be "top dog" in one situation (say, if food is involved somewhere) and the other dog may be the "top dog" when outside on walks, or over other resources such as toys

Sometimes it's obvious who is who, but not with all dogs and perhaps yours just come into that category where they happily rub along and neither is concerned ...

How lovely that they are like that!!!!!

My crew are exactly this way - fluid. They have different strengths and weaknesses and have things pretty sussed between them for who to look to in different situations. The anomoly would be that one is hearing dog for my deaf crew so I have helped her enhance that strength to a degree but the basic premise [ to my crew ] was pretty natural in that regard.

When my old girl was alive, she was absolutely the leader, ruling with a velvet paw - the truest form of whats considered `alpha`, confident in herself, able to guide the others and with no need for shows of dominance. If they were on the sofa ans she wanted to get up, she only needed to put a paw on it and they would jump off out of genuine respct for her not because they felt any fear of her. She was the gentlist most unassuming dog anyone could ever imagine and her loss devastated them as well as me. For a while they were all in a quandary, as she`d been their `gel`, so I just let them work things out for themselves, with no pressure on any of them to do what she did, and without me stepping in and confusing them, [ they get along fine btw, there was no dominance/change of heirachy issue as a result of her passing away ], hence them settling in to utilising their best areas individually in ways which compliment them as a family group.