* Invest Yourself: The Catalogue of Volunteer Opportunities, Susan Angus, The Commission on Voluntary Service and Action, Box 117, New York, N.Y. 10009.
* Volunteer, Council of International Educational Exchange, 205 E. 42d St., New York, N.Y. 10017.
* Directory of Long-Term Voluntary Organizations, Voluntary Services Publications, UNESCO, 1 Rue Miollis, 75015, Paris, France.
* Directory of Volunteer Opportunities, Ellen Shenk, Volunteer Directory, Career Information Center, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
* The International Directory of Volunteer Work, David Woodsworth, Vacation Work Publications, 9 Park End St., Oxford 0XI 1HJ, England.
We're going to Venezuela and plan to stay at a resort camp called Canaima, near Angel Falls. Where can we get information about it? D.M., Harleysville.
Canaima is located in the jungle of Southern Venezuela near Angel Falls, the world's highest waterfall with a drop of 3,181 feet. The resort is not luxurious, but fairly comfortable, considering its remoteness.
You can begin by contacting the Venezuelan Consulate in Philadelphia at 923-2905. The tourist packet that the consulate sends out includes a small amount of information on Canaima.
Another source is Avensa Airlines, the Venezuelan national carrier that operates daily flights to Canaima from Caracas and can be reached at 212-956-8500.
Canaima sits on the edge of a lagoon, with waterfalls and eerie, flat-top mountains nearby. Angel Falls, however, is miles away, and many Canaima visitors never even see it except from the air. In good weather the Avensa pilot may detour past the falls before landing at Canaima. (Sit on the right side of the plane for the best view.)
Airline seats are often so cramped. Could you tell me what seat to request by the exit where there are no seats in front of you? R.F., Croydon
Although airplane models vary widely, certain seats on any flight have more legroom. Getting into one depends on your knowing what to ask for, reserving far enough in advance, and luck.
The ones you ask about are called "door row" seats, and while they definitely feel more open, sometimes the flight attendants make preparations there and the galley area sometimes attracts passengers who like to hang out on long flights.
Bulkhead seats are behind partitions, and their advantage is that there's no seat reclining in your face. Thanks to a bit of extra room, the same is true for seats in emergency-exit rows.
Most of the airline's frequent-flier programs offer seating charts of their aircraft that can help you pick a seat, and being a member of one of those programs can sometimes help you get a preferred seat.
Several manuals for airline passengers have seating charts, too, as does the Airline Seating Guide, published four times a year by Carlson Publishing Co., Box 888, Los Alamitos, Calif. 90720. The U.S. edition costs $39.95 a year.
The airlines sometimes reserve bulkhead seats for passengers who need assistance or have children, so they may not become available until the last minute.
To increase your chances of getting one of the roomier locations, ask at the time you make the reservation for a seating assignment. If seating assignments aren't available, make your reservation but try again later for advance seat selection.
I would like to get information about trips on freighter boats, such as how much they cost and where they leave from. A.L., Collingdale, Pa.
A good source is Freighter World Cruises Inc., which promotes itself as the largest travel agency in the world dedicated to freighter travel. Its bimonthly newsletter, Freighter Space Advisory, has schedules and photographs of freighters, including the accommodations.
Contact Freighter World Cruises at 180 S. Lake Ave., Suite 335, Pasadena, Calif. 91101; 818-449-3106. A subscription is $27 a year, but the company will provide information and a sample issue at no charge.
Also useful would be Ford's Freighter Travel Guide, 1988-89 ($8.95); contact Fords Travel Guides, 19448 Londelius St., Northridge, Calif. 91324; 818-701-7414.
Donald D. Groff welcomes questions from readers and will reply to each. He will answer those of general interest in this column, and others by mail. Send questions and a self-addressed, stamped envelope to Donald D. Groff, Travel Department, The Inquirer, Box 8263, Philadelphia 19101.