How to measure product backlog

If you want to estimate how much work is in a Product Backlog, wouldn’t it be best to ask the Development Teams who are likely to do  it?

Correct but i don't know which team is going to take this items and when.

how can i measure it how much job size or SP's work is present

In your opinion who should do it ? If you know answer to that then there you go :-)

some items i might take some years later.

Very Interesting!! Why do you think these items will still be relevant some years later ?

I agree with Ian, the Dev team should be the deciding factor for sizing and estimation. Also, is there any way to break down these huge items into a few smaller tasks? I know that depends fully on the individual backlog item but I have seen with the scrum teams I've worked on that initially an item is measured at 100+ but through further discussion it was able to be broken down into 2 or 3 different items. Something to consider for sure.

One way to get rough, high level estimates is to teach the Development team relative T Shirt sizing and Affinity Grouping. 

Keep in mind that early on the team knows the least about what they are building, so forecasts are not very accurate Through inspection and adaption, and progressive enhancement of the Backlog items and estimates, you can take the learnings and adapt your release plan over time.

Plan to re-plan!

Mirroring Chris' statement as well. T shirt sizing works very well. When I was at Harley, our scrum teams changed it from T shirt sizing to models of the bikes. So a small would be a Sportster, Medium a Dyna, Large was a Softail, XL was Touring, and XXL was CVO (the super expensive custom baggers). This made it fun and relatable since it correlated with the product and was well known by the Dev Teams. I wanted to call that out because I've heard from some SM's that say their Dev Team doesn't do well with T shirt sizing but changing it to be related to the product of their company really helps. 

+1 Curtis.   Thank you for that observation.

Correct but i don't know which team is going to take this items and when.

Estimates by their very nature involve uncertainty. To get the best current estimate regarding the size of the Product Backlog, what forecast can be made about the kind of team or teams which are likely to do the work? Do they have previous experiences which they might be able to draw upon?

For the level of uncertainty to be reduced, how might the likelihood of a suitable team doing the work be made more certain?