With those leaves probably one of the Syringa x prestoniae selections. Regarding pruning what are your goals?
I agree with previous question by RonB re: pruning goal If it’s like an old lilac in BC regions in ghost town areas along old farm field or railroad - you could go as far as taking a chainsaw to it - and it’ll come back with new green leaves (no flowers for a few years) (yes a house contractor did that to one of my old garden shrubs - the shrub lived and looks great now ) So that’s why RonB asking your pruning goal (to be considered in context of the photo id provided ) That’s an interesting history for that ID Syringa × prestoniae | Landscape Plants | Oregon State University
Here are 2 different options for restorative pruning of lilacs: Pruning Large, Overgrown Lilacs | Horticulture and Home Pest News
Good article - Lilacs are tough survivors It appears as though the subject in original post has been sheared - and possibly has had the « next year’s old wood » removed (in other words, for example, the blossom for 2022 (yes 2022) will appear on new growth happening now, June 2021 - so if one shears the lilac too late in 2021 - you may observe less bloom than hoped for in spring 2022. (My very non tech explain ) —— I have done the « one third per yr over 3 yrs » on straggly rhododendrons - and it worked well (on the other hand, my neighbor goes for 100% in one year - it works too!)
