asuming you have root access for the server:

# place a nginx config file that gets read for all domans

$ vi /etc/nginx/conf.d/enable_gzip.conf

place following content

# Enble Gzip
gzip  on;
gzip_http_version 1.0;
gzip_comp_level 2;
gzip_min_length 1100;
gzip_buffers     4 8k;
gzip_proxied any;
gzip_types
# text/html is always compressed by HttpGzipModule
text/css
text/javascript
text/xml
text/plain
text/x-component
application/javascript
application/json
application/xml
application/rss+xml
font/truetype
font/opentype
application/vnd.ms-fontobject
image/svg+xml;

gzip_proxied        expired no-cache no-store private auth;
gzip_disable        "MSIE [1-6]\.";
gzip_vary           on;

check for errors in config file(s)

$  nginx -t

reload nginx config

$ service nginx reload

verify

 curl -I -L -H 'Accept-Encoding: gzip,deflate' https://yourdomain.tld/static-file.static