1) please refer to figure below. i have two vias to ground in schematic but when i click "generate/update layout" in translate to one via in layout which is wrong. how can i generate two vias in layout?
You have placed two vias in parallel in schematic, and you get two vias at the same position in layout. Just move them as needed.
2) does ADS have any layout component for DC supply? please refer to figure below.
It is easiest to draw a pad yourself.
3) the whole point of me doing layout in ADS is to correct the layout if in case its affecting the circuit performance. after generating the layout, how can simulate the layout? Am i need to simulate the layout in EMDS/momentum and then create schematic component and simulate that in schematic by connecting lumped element? any short cut way? im using ads2015.
Yes, you can use results from EM for the layout for the parts that have no schematic model (easy) or for the full layout (requires more EM experience). This is your engineering decision.
4) how to release gerber in ADS?
In layout, export artwork in File menu.
how can generate multilayer PCB in this case. i need to generate 8 layer board.
The microstrip parts that you have shown are on the "outer" layers? And you will take it into a "real" PCB" layout program to combine it with digital circuit that needs 8 layers?
how can use MSUB to do it? In ADS cond and cond2 are default conductor layers. what are the 3rd, 4th, 5th, 6th, 7th and 8th conductor layer i can define using MSUB?
Micorstrip is for one conductor layer over a ground plane. In a multilayer, these are the "outside" layers on top and/or bottom. The inner layers are usually not drawn in ADS.
how to define my 7 dielectric layer? i need to choose the name of the layer from ADS layer list as below? please elaborate since im confused in this area
I would use Momentum and run things in Momentum
if there is coupling between layers and multiple dielectrics needed. But for microstrip we typically have that ground plane that shields the top conductor from everything below the ground plane. Then you can simulate them separately.
6) Ads have 255 layers!!! this so many layers confusing me! is it means whatever layer i define in MSUB only will be used? all other layers will be neglected?
Even if you have 8 metal layers, every layout system has more than 8 drawing layers. There are extra layers for solder mask, component print and other functions. So the number of layout layers is larger than the number of conductor layers.
In ADS, the predefined layers also include layer names for 8-layer PCB: pc1, pc2, pc3, ... and pcvia1, pcvia2, ...
This is because ADS designers want to give you a choice what layer names you want to use. But these are only names, and there is no difference in functionality. You can use "cond" or "pc1" and the difference is only the name. You can use (almost) any layer name - just map it to the correct physical position if you are using Momentum.
Now that you have an idea how to start, it is a good time for a Keysight ADS training. These are really good to learn more about the tool and workflow.