Это ошибка, которую я вижу
D:\Knowledge Base\ion_knowledge_base> jekyll serve
Your Gemfile lists the gem jekyll (~> 3.8.5) more than once.
You should probably keep only one of them.
Remove any duplicate entries and specify the gem only once.
While it's not a problem now, it could cause errors if you change the version of one of them later.
Traceback (most recent call last):
12: from C:/Ruby27-x64/bin/jekyll:23:in `<main>'
11: from C:/Ruby27-x64/bin/jekyll:23:in `load'
10: from C:/Ruby27-x64/lib/ruby/gems/2.7.0/gems/jekyll-4.0.0/exe/jekyll:11:in `<top (required)>'
9: from C:/Ruby27-x64/lib/ruby/gems/2.7.0/gems/jekyll-4.0.0/lib/jekyll/plugin_manager.rb:52:in `require_from_bundler'
8: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler.rb:149:in `setup'
7: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/runtime.rb:20:in `setup'
6: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/runtime.rb:101:in `block in definition_method'
5: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/definition.rb:226:in `requested_specs'
4: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/definition.rb:237:in `specs_for'
3: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/definition.rb:170:in `specs'
2: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/spec_set.rb:80:in `materialize'
1: from C:/Ruby27-x64/lib/ruby/2.7.0/bundler/spec_set.rb:80:in `map!'
C:/Ruby27-x64/lib/ruby/2.7.0/bundler/spec_set.rb:86:in `block in materialize': Could not find nokogiri-1.10.5-x64-mingw32 in any of the sources (Bundler::GemNotFound)