How to have comprehensive knowledge of other disciplines?

I cannot comment on the role of a cost engineer, but as a planner it is not your job to have comprehensive knowledge of other dsciplins and what you think about duration and sequence is largely irelevant.  Good planners work with the project's managment (at all levels) to develop a schedule that accurately reflects how they intend to achieve the objectives of the project (time, cost, quality, safety, etc.).  The skills needed are in the areas of listening, questioning and influencing, linked with a thorough understanding of scheduling theory and the tool you are using. 

You will find most dscilpine experts thoroughly understand their bit of the project, your primary function is to manage the gaps and interfaces between the different dsciplines to crate a comprehensive and sealess plan that fits within the overall project objectives. 

There is a lot of material you may find useful in the GPCCaR on this website and on my website at: https://mosaicprojects.com.au/PMKI-SCH.php

if you can read the other specifications that would be good also, BUt one thing to do is to go out into the filed and look at the other work being performed and ask questions so that you can learn. Cross multi discipline training is a very valuabel tool for you and the copmany to have. This goes for other departments as well such as design, accounting, estimating, procurement, safety, quality, etc. spending a little time in each of these departmes can be very beneficial to understand how each department works and then it is easier to see the inter-relationships between them and how the company works as a whole.