Here i am showing code for migx within another migx in Modx Revolution
BackEnd :
first you have to written below code in "Form tabs" when you create migx TV in which you want to show another migx,
{"field":"institutions","caption":"Institutions","inputTV":"another_migx_name","renderer":"this.renderChunk"},
this will create another migx inside your original migx and store values in it.
FrontEnd :
now in frontend in main migx write simple migx code for fetch values from main migx.
[[!getImageList?
&tvname='migxTVname`
&tpl=`mainChunkName`
]]
in another migx for fetching values you can write like this code,
[[!getImageList?
&value=`[[+institutions]]`
&tpl=`Chunk_name`
]]
now it's done, and it will show your inside migx values.
If this helps you comment it and share it.