How to fetch data when click for button?

[zaidali]

Hello everyone
Can someone give me steps for create button in my document ,and when click for that button can fetch drug table from patient encounter to current document
like this

[taher_zaq]

frappe.run_serially([
() => frappe.timeout(1),
() => cur_frm.doc.field_name_in_new_doc = frm.doc.fieldname_in_prev_doc
])