There are several ways to identify US made 1934 junk dollars. In general, there are two versions of the US mint 1934 junk dollars, the "Philadelphia", and the "Taiwan restrikes". The Taiwan restrikes are likely to be made in the USA during 1949 while the Philadelphia ones were made in the 1930's till around 1945-46.
Here are the features for the Philadelphia strike:-Pimples.
-Wide rim.
-ribbon behind neck (some of them).
Here is an example of the "Philadelphia" version of the 1934 junk dollar:
Here is the pimple feature:

Near where the nose is pointed at there is a pimple, there is also a pimple right between the Chinese "2" character. These are the best identifying features for the US mint version.
In addition, the rim is really thick compared to the non-restrike central mint versions

Left is the US mint, right is non-restrike central mint.
The second image is another "Philadelphia" mint though it is a earlier strike because the ribbon is still intact.

You can see the ribbon on the right side of the bust on the neck. That is actually a strikethrough of the ship's design. This only exist in earlier strikes when the dies are fresh.
"Taiwan restrike"The Taiwan restrikes were a result of the Nationalist retreating to Taiwan and brought with them the last baatch of 1934 junk dollars that were either made in Shanghai during 1948-1949 or were made in the US in 1949. Their first appearance in the market was in 1999 when 6,000 coins were sold in batches. Due to the long time they were sealed in boxes nearly all of them are in high grade blast white condition.
Features of the "Taiwan restrikes" are: -Thick rim.
-curved waves.
-no pimples.
-blast white (least reliable).
Image below is a "Taiwan restrike" version:
Apart from the previously mentioned thick rim, there is also no pimples that is part of the "Philadelphia" version.
In addition, the Taiwan restrike version also has waves that caved inwards as shown in this image:

Left is a Taiwan restrike, right is a central mint restrike.
For both the "Philadelphia" strike and the "Taiwan restrike", you must take into account all these features to make an educated guess because there are many variations of these features. However the features I mentioned above are the best features for identification.
At the end of writing I realized I should have made it a new post rather than answering a question, but too late I suppose.