My 10yr old JRTxSpaniel has seemed not quite herself the past few days. She doesn't seem as bright and has stopped wanting to come on a walk in the morning. She seems to gear up about midday and is still eager as anything to come out for the second walk and still plays like a lune then, but she's definitely a bit off.

Sooo, when I take her to the vet what should I ask them to be checking?
Normally I've got a fair idea of whats wrong with a pet I'm taking in so feel quite confident in asking questions etc. but I have no idea what the vet should be checking in the case of low energy levels and general sluggishness.
I feel a bit ignorant and confused right now :s

i can't give a lot of advice but i would ask the following-:
check her body all over for any discomfort + ears and mouth.
listen to her heart.
maybe a blood test if the vet thinks it would help and theirs no obvious signs of any problems by looking over her.
also maybe a urine test.
A blood test should pick up any problems with liver, kidney etc.
Alot depends on whether your vet thinks certain tests are needed or not but you may just find it's her age catching up with her even thoug she's got a good few years left.

I would say the same:
listen to chest
check eyes,
ears,
bottom,
and general palpation
generic blood test (Something I done every year in an elderly dog anyway, some say waste of money but for my peace of mind)
Urine dip

I take my old girl twice a year now she is nearly 16.
I have eyes
ears
bum
heart,
lungs
unrine test
blood test
and anything else that i think there may be a problem with.

Very lucky so far just a few fatty lumps

But defenatly worth doing.

Peanuts

worth you giving her a gentle feel over in the morning and see if she is sore on back or leg joints.  if she is stiffening up overnight that would make her a little slow in morning till everything loosened up again